Hi,
The short answer is: for dialing calls your phone behaves like a local phone while for people to call you they must dial your number as if you were in the US. In other words:
-to call your friend dial 00 352…
-to call the UK cab dial 0787 123… (when dialed from within the country all UK numbers have a zero in the beginning)
-and a bonus: your friend will dial 00 1 484.. to call you:)
Hope this helps.