Odds are, you could easily get by on a barebones AT&T MVNO based PAYGO account (Airvoice/Jolt or PureTalk) if you get your data in check (which it sounds like it should be easy enough). $15/month with PureTalk would get you the Simple 80 plan plus 400MB of data (given it's a wildcard), which would just cover your average usage with very little wiggle room. That margin could be opened up further using XMS, Kik, Hangouts, etc. as you pointed out. Otherwise, you might be able to get on board the Airvoice $10/month plan with sufficient data discipline, which would also give you rollover credits. And of course, P'tel is always an excellent option if T-Mobile coverage suits your needs.
The only problem may be the phone itself. The GSM slot is carrier unlocked as Shade pointed out, but Verizon might have gimped the firmware to prevent you from setting GSM APN data settings on the thing. If they did, it'll likely require you to stick Cyanogenmod on it to get the functionality back. Of course, if you could get by without mobile data this would be a moot point.
Otherwise as of currently, if you want to stick with a Verizon MVNO, your only option right now is Page Plus given it's an LTE handset. It also means you have to commit to at least $30/month, which is ridiculous overkill for your needs. Selectel should be getting the ability to do LTE soon, but it's unknown if they'll be permitted to activate LTE handsets on their cheaper plans or not.