First, it should be explained that in the old days, NTT was owned by the Japanese government, and they pretty much owned the telecommunications market.  In order to foster competition, the government spun off NTT and mandated that they allow access to their infrastructure to competitors.  This when you buy Flet's internet service, you get (at least) two parts:

1. Physical line/infrastructure (Provided by NTT Communications East/West)

2. Internet Service (Provided by the ISP or "Provider")

You may also have phone, TV, or file backup/storage service, etc. which runs over the internet, which may be provided by #1 or #2 above, or some third part (like Hulu, UNext, etc.)  You may also have other contracted services related to #1 or #2.

In the case of Flet's, the "Pure" NTT solution is Flet's + OCN internet, where OCN is a subsidiary of NTT Communications.  Even when using only NTT, however, the line lease and internet service are still separated out, and technically provided by separate companies, so this makes things more complicated when signing up for or canceling service.

Besides OCN (a subsidiary of NTT), you can also use So-Net (A Sony subsidiary), @Nifty, Yahoo BB, and others.  In most of these cases, unless you prefer separate billing, NTT East/West will handle the billing.  

Note that Sony also provides their own Fiber service where they run the infrastructure, which obviously uses So-Net for internet service.  (This service is called "Nuro" and supports up to 2GBps, but only to small apartments and separated houses in Eastern Japan, no apartment complexes for now.).

KDDI (Au) also provides their own 1Gbps FTTH internet service, however it should be noted that it is available only to existing Au Cell Phone customers.

We will cover the Flet's OCN from NTT East service here, since that is what we have experience with.  

The first thing to note is that for personal service, there are two types:

1. "Mansion Type": This is for condos and high rise apartments.

2. "House Type": This is for separate houses and small apartments.

The cut-off changes from time to time, but if you live in a separate house or old split up wooden house being rented as apartments by the owner, you can expect to fall under #2 above.  If you live in a fancy concrete building with more than four floors, you can expect to fall under #1.

The practical difference is this:  If your house has a centralized wiring closet where all the telephone connections and such come in, then you fall under the "Mansion" category.  If not, then you fall under "House".

Why the difference?  

Mansion Type

Essentially, for large apartment buildings with wiring closets, NTT East/West will install a fiber line for every 10 people and split up a 1Gbps line into 10 100Mbps contracts.  Because of this, and the fact that construction work is usually minimal or non-existent, this service is cheaper.  In such apartment buildings, very high speed short distance DSL is often used between the wiring closet and each apartment, such that 100Mbps can be achieved without running fiber or Ethernet.  Some apartment buildings have Ethernet already installed, and that is used.

House Type

For house type, connections, a 1Gbps line is run, and sold directly as a 1Gbps line (NTT West) or 200Mbps (in the case of Hikari Next) line (NTT East).  If multiple people in the same apartment sign up for service, a separate fiber is run for each person - hence the higher cost.

Construction

Typically there is a construction cost charged for new connections, which can be around 9500 JPY (Mansion) or 24000 JPY (Mouse) can be split up and discounted over a 2 year contract.  If you move to a new house in the service area and apply to have your service moved to the new location, you don't necessarily have to pay again.  This is called "Construction" even in cases where all they do is deliver a router, since they don't necessarily know ahead of time whether any additional work needs to be done or not.

From the time you sign up until NTT can come to work on the construction will be about a week to two weeks.  They can come on the weekend if you prefer.  For Mansion type connections, you must make sure than the landlord or property manager is available to unlock the wiring closet if applicable.  For House type connections, make sure you ask the owner's permission if you are not the owner.  

For Mansion type connections, the "construction" will typically involve setting up some equipment in the wiring closet which converts and transmits the optical signal via Ethernet or VHDSL over a phone line to your room.  Then, they will install a modem, and possibly a router in your room to receive the signal.  (Sometimes this is one unit, sometimes multiple units.  

For House type connections, slightly more may be involved.  In general the fiber itself will be run into the room, which requires a place for it to run.  If it can be done via existing telephone wire entry points, they will be used.  (This method is of course the nicest looking).  If not, the holes created for air conditioner pipes will be used.  Finally, if that is not possible, they will simply drill a new hole in the wall, run the fiber in, and waterproof the hole.  It's not pretty, but it works.  

Either way, with the fiber in your room, the NTT technician will install a modem that can convert the optical fiber signal into Ethernet.  This may or may not include an integrated router.

In either case, WiFi may or may not be an included feature, but you can always provide your own WiFi router).

The technician will help you set up the router and any computers you have on premises for free. (within reason).  Don't expect them to touch computers with an English OS, or exotic configurations, though.

Basically, if you know your way around network configuration, you can handle this yourself.  In the case of OCN, you must use PPP over Ethernet to get an IPv4 connection.  If you don't know what this means, it means that you have to "log in" to the connection before it will work, so this information basically has to be entered into the router.  OCN (or whatever provider you have chosen) will send you this information before construction day.  If you sign up for IPv6 with OCN, you can use that directly with no PPPoE, and the 200 Mbit speed limit does not apply, so a max of 1Gbps download is available for IPv6 sites.

Basically speaking, if you set up the PPPoE on the router, then you don't have to set up much of anything on your individual PCs.  Apple's Time Capsule router works perfectly fine for connecting to PPPoE and distributing the connection to individual PCs.

The standard OCN home service does not provide a static IPv4 IP address, each time your PPPoE connection is re-established (for example, if you reboot your router), the IP address will change.  

Limitations:

1. Download - OCN claims unlimited downloads, and they seem to mean it.  We downloaded a backup from an off site server comprising of several hundred gigabytes, and received no complaints.  Since examples of acceptable usage include watching video and streaming audio, it seems unlikely you will receive complaints unless your usage is truly excessive.

2. Upload - OCN has an upload limit of 30GB per day.  If you go over this limit frequently, they will warn you, and then disconnect you.  They give as an example "You can upload over 4 DVDs (4.6GB) per day" without hitting this limit.  The usage scenarios likely to go over this limit seem to include Online Backups, and BitTorrent.  For Online backups, one could probably simply limit the upload speed so that you stay safely within the limit in any 24 hour period.  For BitTorrent, similarly, you might want to limit your upload transfer speed.

For those interested 30 GB per day works out to 21 MB/Minute or 35 KB/Second. (That is in Bytes, not Bits.  Multiply by 8 to get bits)

The upload limit was 25 GB a few years ago, so it is likely that it will be raised again as time goes by.  

Outbound SMTP is blocked for spam prevention reasons, so you'll have to authenticate and use OCN's mail servers.  This should affect only those who wanted to run their own mail servers. (i.e. mainly Unix hobbyists).

Related Services (OCN):

1. OCN comes with a mail address, which can be accessed via clients (via PPP or ActiveSync) or WebMail.  The format is xxxxxx@yyy.ocn.ne.jp, where yyy  is automatically chosen and contains subdomains like "ray" and "hyper".  

2. OCN comes with access to OCN's mobile hot spots (i.e. WiFi spots scattered around Japan).  Note that they will send you the login information before construction day along with the land line information, and you can use it without applying - however, if you use it, you will be billed up to around 3500 JPY per month.  You can sign up for unlimited use for 300 JPY, so try it out to see if you really want to use it and then sign up if it's useful to you.  (Note that confusingly, this is different from Flet's HotSpot, which is offered by NTT Communications!)  I find that OCN hot spots are less plentiful than NTT Flet's Spots.  You can use your OCN HotSpot login information as soon as you receive it, and if you switch your plan to the unlimited plan it takes effect immediately.  The SSID you usually connect to will be "mobilepoint".

3. OCN offers an MVNO service through Docomo's infrastructure called "OCN Mobile One" marketed towards providing light duty internet for Smart Phones starting at around 900 JPY per month.  If you want to use this, you have to sign up for it separately, though if you sign up for it through your existing OCN account, you will receive a package deal.  (If you sign up, they will send a SIM card in the mail).  

4. MyPocket - this is a file storage/photo album cloud service offered by OCN.  There is a backup client available.  They seem to offer the first 65 GB free and offer and upgrade to a 256GB plan.

5. IPv6 - You have to sign up for this with OCN if you want to be able to use it, and it has to be enabled with NTT first. 

6. Hikari Denwa - This is a phone service you can use with your land-line connection.  Basically it's a land-line VoIP connection.  It will come with a router that has a normal phone jack, so you can connect a normal corded (or cordless) phone and will come with an 050 number.  Calls made from this number will be cheaper than calls made from a normal (03, 07, etc.) home or office land line.

Related Services (NTT):

1. NTT HotSpot.  This separate from the OCN hot spot option, and you have to sign up separately.  Once you sign up, it takes about a week to provision, and they will send you the details, including password, etc. by postal mail.  The SSID used by this service is usually "NTT_SPOT".  For existing NTT customers (including anyone with Flet's), the cost is only 200 JPY per month.

2. Flet's Azukeru - This similar to the MyPocket service above, except again offered by NTT instead of OCN.  This one seems to offer only 5GB for free.  

3.  (New Hikari Next Connections automatically support IPv6, but older Flet's B customers may need to apply).  

4. Hikari TV - The connection is fast enough that TV can easily be piped over it.  Hikari TV is a Cable TV type service that uses the connection at a low level and is thus available only to Flets customers.  (You can use higher level services like Tsutaya TV, Hulu Japan, U-Next, etc. with any internet connection, including Flet's).

5. 050+ - This is not directly related to Flet's, and is one area in which NTT and OCN cooperate rather than compete.  050+ is a smart phone and PC (Windows/Mac) application that works similarly to Skype, which will give you a Japanese VOIP number.  The quality is in general much higher than Skype and/or Line and calls to other 050 numbers are free.  Calls to Japanese Cell phones and land lines less expensive than typical plans.  There is a base fee of 300 JPY per month, plus usage charges.  It is mentioned here, because if it is purchased with OCN services, a discount applies.  In fact, one can use a mobile one SIM in combination with 050+ on a smart phone to have mobile internet and calling for less than 1200 JPY per month base, and competitive per month rates.   

Speed test:

About speed claims... I managed to get over 190Mbps more than once on speed tests using a newer router and a computer with Gigabit Ethernet.  If you are using an older router or slow wireless, don't expect that much speed, as your router may well be the weak link.  Also, many older computers have 100 BaseT Ethernet, which again will slow things down.  Bear in mind that even if your speed test shows 200Mbps, that does't mean that most web sites can actually send data at that speed.  Normally you will receive around 20,000 JPY cash back (or store credit) for signing up.  Use that cash to buy a new router, etc., if necessary.  If you plan on using wireless and your computer doesn't have Wireless AC, you should consider upgrading your wireless card as well.