I'd really like to see femtocell on T-Mobile. Every other U.S. carrier (AT&T, Verizon, Sprint) have it or are going to have it soon. UMA doesn't appeal to me, because it limits the handset choices. I want to be able to use whatever handset I have (and keep my choices open), but improve my home reception.
I just moved and my reception at home is pretty spotty now. It's the first time I've ever had problems with T-Mobile (and I've been with them since the Voicestream days). I really don't want to switch to AT&T, just so I can keep using my GSM handset. AT&T has the worst customer service of any company I've ever dealt with, many times over (I used to have an AT&T landline). Femtocell would be a good solution for me.
Alternatively, I'd be happy if I could use the wifi on my phone to access my T-Mobile service. I have a Symbian S60 device, with VOIP capability. But it seems like hotspot@home only works with specific UMA designed phones.