Not every GSM carrier roams on every other carrier. Case in point- I could not roam on ACT GSM in Thailand despite them being the ONLY carrier outside the Americas using the US 1900Mhz GSM band! Roamed just fine on everyone else tho. NPI wireless is a regional player and I'd be unsurprised to learn they don't have very comprehensive agreements. Haven't seen a list of their partners, no. It's something they should at least be able to fax to you.

Yep, GSM geek. Fun is doing network searches on approach into SIN. The game is to get the most networks possible. Between 3G and GSM, that's a BUNCH of networks.