[GadgetKen]

No international prepaid gsm sim card has great rates everywhere, 100% reliability on callbacks plus data on any device, and sterling customer service...and yes I wish there was such an animal. The underlying carrier or the roaming clearinghouse they use can negotitate good rates with some carriers but not with others. Agree a Maxroam, Celtrek or Yackie local number is good. Data is available currently on some internationals sims(Mobal, United Mobile, Maxroam), but not sure how many callback sims, if any, support Blackberry devices. Incidentally I heard on NPR that for President Obama's Blackberry, they needed to route it through White House computer servers, and implement other security measures on it.

Think realistically the best solution currently is an assortment of prepaid sims (international, regional, or country specific), a prepaid landline calling card good for cheap calls from the country you are in, some change to feed into a payphone, a small wifi device or laptop with mobile phone data capabilities (GSM or other digital standards), and for those with maritime needs or traveling to way out of the way places...a satphone.