Got my Nexus 7 GSM today.
Cut up my full sized sim to fix into micro sim slot. Worked fine.
Inserted SIM into tablet. Got signal. So far so good.
Nexus 7 doesn't have Phone.apk or MMS.apk on launcher.
Fired up Wi-Fi, went to go Play Store.
Installed Go SMS Pro.
Set up my sim card online. Activated with $30 100 minutes, UL txt, 5GB plan.
Had to retry "nearest city" options and zip codes, but eventually got it to work.
Got my SMS notification on my tablet saying account is good.
Refilled for a month.
Got my SMS notification of the refill.
Setup a T-Mobile account with my prepaid number. All good.
Reboot tablet. I get "Sign into network" which is a html redirect page.
Every page redirects to sign in page. Can never sign in.
Turns out it's detected as a tablet. IMEIs are apparently flagged by T-Mobile.
I'll root and mess around my /efs/nv_data.bin and reboot back, but so far :-/
Edit: No /efs folder