blackberry 8830 with global sim chip

[kmetech]

we are going to use our phones (got the verizon vodafone sim chips )in ireland will we get a local  an irish vodaphone number when we arrive (if so how do we find out what our roaving number is)  if not how do we have to dial 086,087 numbers as though we are in states ?and conversly does a irish cell number have to call our our usa cell number to reach us?