I'd say pick up the $10 card and a $1 SIM and give it a shot, then. If it works out, and especially if you start using GrooveIP a lot when in WiFi signal areas, that $10 card might well last you the three months until it expires.
I mentioned this on another thread, but I'll repeat it here - if you ever decide to add data, keep in mind that T-Mo doesn't offer data on their "partner"/roaming networks, though they do offer voice and SMS. But if you decide to start getting into data, it might be time to look into AT&T-based StraightTalk or something, and the Nexus 4 will support that just fine. Or if you live in a pretty urban area where T-Mobile is offering the service, you'll be fine.