Looks like there are some new phones headed T-Mobile To Go's way. Best Buy (http://is.gd/rUL) has a few models that I've talked about before...the Nokia 1208 ($30) and the Nokia 2760 ($70). The 1208 is comparable to the 2610, it seems...maybe a little cheaper on T-Mobile's side. The 2760 is your typical Bluetooth camera flip low-end phone.
In other news, you can get internet on T-Mobile To Go...but you have to go to Mexico or Canada to do it. In canada, it's a pretty penny (well, a penny and a half) per kilobyte and in Mexico it's $0.01 per KB. However it's cheaper to talk in Canada than in Mexico, with roaming rates of 69 cents per minute versus $1.49. You're better off getting a SIM in that particular country, but that's assuming your phone is unlocked, which it may or may ot be.
Also, MMS (if it's available) doesn't cost anything extra in Canada or Mexico vs. what it costs here. Neither does texting in Canada; 10 cents to send, 5 to receive. In Mexico, and in elsewhere, text messages are a whopping 35 cents to send, though still 5 cents to receive, apiece.
I still don't understand why T-Mobile To Go doesn't allow data access beyond their free (and admittedly okay) T-Zones.