Lol, I can go to the Blackberry or Crackberry forums, and there are long running threads from users who switched from Blackberry to Android. Not even the iPhone has ignited this level of controversy.
While the Droid does lack GSM, you can't use prepaid SIMs on the Tour or Storm unless its Vodafone's. That means you have to roam, which means paying for expensive data and so on. Unfortunately unlike the DROID, which still has Wifi, the Tour does not. Pretty much because the Tour lacks Wifi, its usefulness as a travel phone is limited.
As travel phones, I can't get email on the Blackberry without BIS and to get BIS, you need a contract, which you're not getting as a traveler. And its getting expensive if you get charged via roaming data.
If your Blackberry is unlocked, yes, you can use prepaid SIMs, even prepaid data plans, but a generic data plan without BIS means you're not getting your push email and other stuff that makes a Blackberry a Blackberry. And you simply not getting your email at all, unless you want to read them on your slow browser via web mail.
On Droid, on a country without CDMA or without a data plan, you can still hit the Wifi and get your email there. In fact, with the wifi, you can still get push GMail and background sync on other email accounts. This is handy if your hotel or the building you headed to do business has open Wifi. Many coffeeshops and malls have open wifi too. But even if the Blackberry has wifi, remember I can't get my email from the wifi. But Droid does.
If you have a GSM Android that is unlocked, I can take any prepaid data SIM on a country you are traveling, with a standard, no BIS, data plan, and still get my GMail pushed to me and all my non GMail email accessed via interval polling.