How can I track down my ideal mobile phone?

The interactive http://www.myrateplan.com/cellphones/ is great and can assist you with narrowing your choices down to phones with a clamshell form factor, a hi-res camera, Bluetooth connectivity, and an MP3 player — but you'll have to investigate further from there, as I don't see items for expandable memory or your triband requirement.

The new Tmobile samsung t805 i believe it is, does all that except it's a slider, not a clamshell. It's on their site (www.tmobile.com). I have that phone and i think it's the best thing since sliced bread!

I recommend http://www.plemix.com. I've bought 2 phones from them in the past year (1 for me and 1 for my brother).

You can get all sorts of unlocked GSM phones from http://www.myworldphone.com/. I use a SonyEricsson that I got from them with T-Mobile and it works just fine, except I was never able to get it to work with T-Mobile WAP. I believe it will work, I just don't care about it enough to actually sit down and figure it out. As far as making phone calls though, it is all good.

My nokia 3650 meets all of the requirements, but is a candybar. It also has a tres-suck keypad. But I got a used one for $30 on Craigslist. I see that you're asking for a general solution, not a particular phone recommendation. On that, I got nothing. Phonescoop will help, but there's not a very good database with *all* of the fields.

Too bad none of the phone selectors say a thing about reception. It's my number one concern in a phone right now. I'd love to find a way to test a bunch of phones in my apartment from a bunch of different carriers. Maybe I should have a phone party...

You'll pay through the noise, but http://www.importgsm.com/ has a whole slew of phones you can't find in the USA through the carriers. Double-check me on this, but I'm pretty sure Tmo uses the same frequencies as Europe, so if you're getting a phone through either Tmo or Import GSM A) it should work fine with Tmo, and B) doesn't need to be quad-band (not that it hurts). It's only Cingular/AT&T that uses an idiosyncratic frequency.

My Nokia 6882 meets all requirements other than clamshell, perhaps you could lighten up on that. My first phone was clamshell and I thought that was what I prefered, till I got saddled with one I didn't want... and discovered I prefered it. My current make-or-breaks are only that they take the 262892 nokia chargers I own by now and that I never have to put phonebook entries in via T9 ever again. Bluetooth represent, yo!

LG VX8100, check eBAY for unlocked ones.