I believe a letter of authorization signed by the account owner, copy of the account owner's IC and your IC would suffice. Just take all to a TM point and they'll process it. While there, you can even ask for an account transfer to your name, save you further hassles down the road.

Well, unless they've recently changed their MO, still, its not right. What if the original owner left the country or is too ill or whatever to physically be present at their office. I suggest you bypass the phone line and try a more "high-end" TM point and talk to staff there. Usually, they are more receptive to such ideas. As per letter format.... the customary.. I, bla bla, with IC # bla bla, hereby authorize name blabla with IC # ..... to ..... bla bla ... my account. I can be reached at ..... phone number or address for further confirmation if required..... Something along those lines. Its a 1 page affair, signed by you both.

sometimes, I don't understand the troubles to do changes or termination.. it happens to all telco... never an easy task...