So today I went down to the T-Mobile store on Van Ness to get an actual paid plan. The rep, Robb, was very helpful and efficient, and made what I thought might be a painful experience into a pleasant one. I had to phone the store back when I got home to get my number ported over as I hadn't brought in my current Sprint account number, but that was painless as well, and the transfer was completed within minutes.
So after over six years as a Sprint customer (due mostly to boyziggy being on Sprint when I decided to get my first cell phone), I'm now on T-Mobile. I got a plan with 600 "whenever" minutes, unlimited nights and weekends, unlimited data and text messages, plus insurance for $75/month (not including taxes). More than I'm paying now, but more than I'm getting now (300 anytime minutes and unlimited nights/weekends/data but only 100 text msgs/month for $50 + taxes and insurance), and I expected to pay more anyway; even if I'd stuck with Sprint, I would have gotten a new plan with more texts and the faster data network with either Ziggy's hand-me-down Treo 750 or a Palm Pre. (Which Ziggy returned in disgust three days after he bought it, by the way, after months of anticipation.) And the iPhone plans I was looking at were similar in cost.
Also, I didn't have to get a contract; since I already had the phone I planned to use, the rep suggested I just go to straight month-to-month. I'm very happy that he didn't try to sell me on a contract or a more expensive plan than I needed.
Yay, I no longer have to carry two phones around with me. I still miss the physical keyboard on the Treo, but the slim sleekness of the Android makes it worth adjusting to the change. I just wish the battery life weren't so terrible. A spare battery, larger mini-SD card, and proper carry case with belt clip are next on the shopping list.