Allied Interstates keeps harassing me.

Are you saying that he is receiving the calls because they are calling a wrong number due to it being a new phone for him or that he owes a debt other than a credit card and they have already discovered his new number?

I doubt he owes a debt other than a credit card and I'm not entirely sure if they have the wrong number or not, since he just got it activated.

Call his phone service provider and complain about the number that is making the call, if you don't know the number, provide them with the date and time of call, keep a record if it should keep happening and report it. File a complaint against them with the FTC, BBB and your AG also. Make sure you file a detailed complaint with the name of the company you are complaining about, and the phone number from where you received the call. Keep checking back for replies.

Most definitely as Shazzers said - I would complain to the company that gave you the number with his new phone and ask for another number. If they won't change it for free - I read somewhere that you can pay a small fee and have the number changed.

Or if it is just the one number calling several times from that company - you could just block the call.

Allied is hardly at fault for an old number in their system. Simply get their address and send a cease and desist letter, telling them that that is YOUR new number.