making calls from US/using mobile in US

I will be in US (Philidelphia) next week for 5 days and will be making daily calls home. Will I be able to use my mobile? If so, will it be very expensive and what codes do I need to use? I would probably be better to get call card - can anyone recommend one that works well.

I was on west coast of America recently, and I was able to ring home from my 086 mobile using +3531 and home number in Dublin. The plus should be at bottom left of your mobile beside the *.

Billo