Sending phones from UK to US?

hi....i was wondering how much if any fees a USA customer would be charged on a mobile phone shipped from UK....for instance say the phone cost my customer $500 including 3 day shipping,what would they be due in taxes there end? or could i mark differently to save them taxes?

This would be based on the value of the item being shipped and the amount you claimed on the customs forms. And based on the coutry you are shipping to.