Wow, I can't imagine going for three years without a phone in Japan... Well, let's see (based on my experience):
To purchase a phone you'll probably need some if not all of the following things:
Gaikoku Torokusho
Hanko (although I have heard that a signature is acceptable in some places)
Bank acct. (make sure you have your acct. # with you if you plan on having it automatically deducted every month)
Credit Card # (if you plan on paying with that)
Note: I have changed phones a lot since i've been here but the only carrier I use is DoCoMo so I can only speak in regards to them and their policies.
Initially I had thought that I would simply have my bill mailed to my current address and then i'd just take it the local convenience store to pay it off (like my utilities, etc.) but to do so requires a ツ??0,000 deposit upfront. That being said, I chose the most common payment option which was to have it automatically deducted from my UFJ acct. every month. After my one-year contract expired and I renewed, I also became eligible for their Premium club (point bonuses, discounts, etc.).
I also learned that there is in fact a way to get around having your acct. deducted every month as long as you make sure there are insufficient funds to be withdrawn. DoCoMo will promptly send you a bill which you can then take to your local convenience store. You can do this as many times as you like and you won't be penalized although i'm used to the automatic withdrawal now so I just budget it in accordingly.
Btw, it should be mentioned that almost all models (with the exception of a lot of prepaid phones) have an English mode. In terms of pricing plans, generally all plans start from around ツ??,000+. For myself, I choose the next highest plan which guarantees me more free minutes but depending on use (sounds like you'll use it sparingly), you could opt for the cheapest plan and be ok. Minutes in excess aren't really that much more expensive although the disparity is noticeable if you use a LOT of excess minutes. You are also charged for packets sent (I send a LOT of e-mails, sometimes 20/day) but this is again negligible.
I do one-year extensions and since I have already successfully completed my initial year-long contract, should I decide for any reason to terminate my existing one with little or no notice then I only have to pay that month's service plan charge as one-time penalty (about ツ??900). Some contracts, unless you're careful-will dupe you into paying the remainder of the balance in full (total service charges) when you break so make sure you make it explicitly known that you may wish to terminate down the road at some point in time.
A lot of the newer features on phones are pretty nice but in reality they are just a lot of eye-candy and gimmicks imho (TV tuner, audio, waterproofed, etc.) and unless you plan on sitting on a train somewhere or being stuck in an airport for hours on end, I think you can afford to skip all the newest trends. Something I do loike though is the high-quality cameras that are being touted with the latest models. The newest Foma model for instance has a 3.0 megapixel camera with optical zoom but comes with a hefty price tag of about ツ??8,000.
Compare that with the Premini-II I just picked up for ツ??,000 and has a 1.3 megapixel camera with 16x digital zoom. Decent enough for my needs. You of course, may find that you don't even need a camera option but it is nice to have since the images are pretty nice quality and can be uploaded from your phone's memory and or separate stick/card.
What else... Hmm, maybe that's all I can think of for now. Oh, and don't forget that there are plenty of decent, slightly outdated models that you can get for absolutely free. Most of these probably won't be displayed since parlors are small and display space is usually reserved for the newest models. If you go to an actual shop for instance and not just a parlor (think kiosk) then you can usually find a small section of "0ツ?? models.
Anyways, hope that helps. Again, things may be different with the other carriers but I do highly recommend DoCoMo. I've never had a problem to date regardless of whether i'm calling Sapporo, Nagoya, Fukuoka, or back home in the States.