I have a Motorola RZR unlocked Quadband that I use in Ja. with a Digicel sim. My wife uses a T Mobile phone (locked to T Mobile) that uses a sim card. The Digicel sim won't work in it because it locked. However, when I put the Digicel sim in the unlocked RZR I can see both the T Mobile and Digicel network. I can access the Digicel network using the T Mobile network.
I called myself from that phone and the call went through. Only problem was that it cost 105.00 Ja. But the good thing is that I can check my credit and sim expiration date. Also I pretty sure that by using the Digicel sim on the T Mobile sim I can avoid having my number go dormant in times when I'm not in Jamaica.
Well worth the 1.30 US cost.