The 3rd level up manager was supposed to call my this afternoon, so by 5:30 pm, I decided to give T-Mobile a call. After several very annoying minutes with their automated voice system that seemed hard of hearing today, I got through to a regular customer service / technical support person. After hearing my frustrated spiel, she said that the manager in question wasn't in the call center where she was, but she'd see what she could do. She put me in touch with someone who is apparently at least slightly higher up then said manager.
This man assured me that I was getting $100 credited to my account, and, in fact, he had given me that credit while I was on hold. I have checked my balance and confirmed that this has been done.
So, yes, T-Mobile's in the running for whatever cell phone I switch to when I switch. I like the Sidekick's keyboard, but I don't think I can stick with the Sidekick forever, and no company seems to be able to get something quite as good for me.
The G1 is close, but not as easy to hold and use. The Droid keyboard made me blanch. I've heard that T-Mobile will be coming out with cool new models, so we shall see.
I still don't actually have my original bookmarks back on the phone, but this is fairly minor. I recreated the ones I've actually needed to use.