So, I decided to check eBay for one of those Siemens S46 phones just to see if I could get one from non-AT&T (and thus fix my problem, even though I don't want to stay with AT&T, if I can get one of those phones cheap, it will be bearable until I get number portability).
It turns out that there were a couple there for pretty cheap (significantly less than what I asked AT&T to sell it to me for). I bid on one and one. So I should have the phone in 7-10 days.
I'll need to change my plan (probably to a one-Rate one), but that shouldn't be a big deal.
Then I'll be able to use the phone all over (where I _thought_ I would have coverage) until one of my complaints comes through and I can get out of the contract and go with a different provider. ... and if I can't get out of the contract, at least I'll have service that is bearable (and I'll just switch after the contract period is over).