My PagePlus phones seem to work fine here in Saskatchewan, where I live and normally park myself , but I had trouble using PagePlus when I was in Newfoundland three years ago so there definitely seem to be some issues. (My Canadian postpaid phone didn't have coverage in one area of Newfoundland where we stayed, so PagePlus seemed attractive as a temporary substitute. Alas, no.) SaskTel here, Bell/Aliant there.
GSM: SaskTel Canada (postpaid voice + data), Rogers Canada (postpaid data), T-Mobile US, AT&T US, Red Pocket Mobile US, Orange UK, 3 UK, Swisscom Mobile Switzerland, tele.ring Austria, airBalticcard (Estonia)
CDMA: PagePlus US
GSM phones: iPhone 4, iPhone 3G, Nokia Nuron (AWS 3G), Otech F1 (quad-SIM 2G GSM), Nokia E63, Sony-Ericsson K610i, Sony-Ericsson Z310i. All unlocked.