In theory, you can set up your Skype Account using a friend's cell phone for caller ID. You must of course, let your contacts know that the cell phone number that you give them to enter into their cell phone directory is not a valid call-out cell phone number. When you use Skype to call their cell phone, the cell phone number you provided them just links that number to a name (yours). To take it one step further, in theory, have them enter that cell phone number as your fax number, rather than your cell phone number.