I currently have a contract with Verizon. I don't think they're GSM. You were talking about Ship-to-shore lines, but it's not like we can use the cell phone on the boat anyways. I was thinking more like in port.
You're correct, Verizon isn't GSM - they're CDMA. Most of their phones won't work overseas, as almost the entire world (outside of the US) uses GSM primarily. You don't have to cancel your contract with Verizon, you can put it on hold while you're on deployment.
You're right about using the phone on the ship. The only time we were allowed to use phones on the big deck amphib during deployment was while we were in port. The USO usually brought cell phones on board for us to use, but alot of times I just let the young guys use them, because there was always a line. Here's something to consider - you can buy an unlocked GSM cell phone without a contract from
TigerDirect for $50, then just use a prepaid SIM that you buy when you hit a port. If you do decide to go this way, your best bet is to buy one that uses the all the GSM bands (850/900/1800/1900). I don't know what the different countries are using, but if you've got one with all four it doesn't matter.
As for ship-to-shore phones, that's what you can use while underway. The AT&T ones are pricey $1/min and generally don't work with any phone cards other than the ones you buy in the ships store. The first thing I always did was find the location of the POTS lines throughout the ship, and figure out how to dial DSN. MCB Camp Lejeune has a DSN morale line that is an automated system that allows you to dial local & 800 numbers. I used a phone card from Walmart (I think it was 1000 minutes or something like that), and spent less money that way.