I currently have a friend who is on Tmo and has the storm2, while I am not sure if this is an issue others are having, I know he has not been able to use data on his S2 despite having and unlim data plan. I do have other friends who use unlocked Verizon devices on Tmo and don't have any problems. I say, what's the hurt in trying it out? If it doesn't work for you, Tmo offers a fair selection of branded BB's! Good luck!
"All are lunatics, but he who can analyze his delusion is called a philosopher." - Ambrose Bierce (1842-1914)