he is out and without credit, and I'm trying to put some on for him. I can't seem to do it from the t-mobile site.. Does anyone know if it's possible to put credit onto someone else's phone?
You can only top up a phone online if the card has been registered to that phone number.
Have you got a convenience store, supermarket or late night garage close to you? If so it may well have the green 'top up' sign. Buy an E voucher and provide your son with the 16 digit number:
Alternatively many cash machines allow you to top up any phone directly from your bank account.
You can do it on-line as long as you have the password to access the account and input the correct phone number. As far as I recall you can use any valid credit card. You may be overlooking a vital step somewhere or falling victim to the ambiguous website.