It sounds like he is using a card services company (they often limit you to UK clients only) rather than his own merchant services account. I would suggest he looks at the epdq service from Barclays which lets you use a web browser and so avoids the cost of a machine (which frankly is minimal anyway). That way his US clients can pay by credit card again.

I don't understand why he doesn't want to accept US credit cards as it must be good for business, although if he can get everyone to pay by cash it does avoid the card charges.