Tablet Phone?


I live about half-time in US and half-time in Mexico. I'm currently using an unlocked Samsung Exhibit II GSM smartphone, with T-Mobile prepaid no-contract unlimited calling and data in the US, and Telcel prepaid no-contract unlimited calling and data in Mexico. I simply switch SIMs when I go back and forth.

All is well, except I'd really like a device with a larger screen - 7" or 10". Like a tablet, but I want to use it as a phone also.

I bought a Nexus 7 with WiFi + GSM option, and it works fine as a tablet. But I found that T-Mobile supports it only as a data device, not as a phone. I tried Google Voice with both GrooveIP and Talkatone on it, but depending on my location, call quality is terrible.

So my question is .... is there any way I can set up an unlocked Android device with 7" or 10" screen, and use it as a tablet and a phone. (yes, I know a tablet is "too big" to use as a phone, but frankly, I don't phone much and I can put up with that). And I'm price-sensitive, particularly as to monthly charges.