I would second the idea of the prepaid SIM card, although the concerns about not having the number ahead of time are very true.

Two good options to deal with that:

1) Once you get the pre-paid SIM, put your T-Mobile or ATTWS SIM back in and forward your calls to the new (international) number. You'll find the rate for forwarding the call is *much* less than the cost for using the US SIM in a foreign country. And you typically don't get charged for incoming calls on the prepaid SIM. So, while still not really "cheap," it's less expensive, and still pretty convenient.

2) Sign up for an 800 number from www.kall8.com. You can reroute the number instantly from the web. So, before you go, give everyone who might need to contact you your 800 number, and then just forward that to whatever number you get on the prepaid SIM.

I've done both, but personally usually just do option 1. Easier for me, and people trying to reach me.