Here's an alternate idea that I use, since it really looks like all you want is voice access. Buy yourself an international prepay SIM card like one of these: http://www.telestial.com/sim_cards.php
(*not* endorsing those, just a random Google hit). Then, right before you leave on the trip change your voicemail on your real number to say something like "Hello, I'm out of the country. If this is important, please call +0123456789 which is my phone number while travelling internationally - otherwise, leave a message and I'll get it when I return."
Additionally, some providers offer free unlimited BlackBerry packages for international roamers! Here's one from a favourite of mine, Peoples (their prepay SIMs are dirt cheap rates): http://www.peoples.com.hk/p_blackberry_iso.jsp
($888 HKD = ~$114 USD right now). The point of my statement is that sometimes while travelling it makes sense not to use your US sim/provider, there can be other, cheaper choices out there waiting for you.