Used the same setup (except the iPad 3) with a BTC sim and it worked fine. IIRC, the sim was $15 and 1GB 4G/LTE was $20/month. After 1GB it's unlimited on EDGE. Coverage in the Exumas
was good for EDGE, whereas the higher speeds were elusive, where you would think highspeed is available it's non-existant, but EDGE is fine for email/gribs and such. I found WiFi even more elusive.