Did Any One Try Using Skype on 3g Networks or on a Phone, Like Blackberry? Free 3g Calls on Skype or Voip 3 G?

I’m trying to find out if skype / voip will work on 3g networks using a blackberry or any other 3g phones over a data plan through T-mobile. It is dollars a month for unlimited data. Did anyone tried making calls over 3g networks? Thank you.