If you are like most people with a bit of sense, you'd assume that was spam and would ignore it. Big mistake according to the user's account. By not replying, he apparently agreed to a $9.99 charge by a company called 41463GamerData_8668958697 on his T-Mobile phone bill. After spending quite a bit of time on the phone with T-Mobile's customer service, they never reversed the charge, claiming they had to pay the company as part of some third party billing arrangement between T-Mobile and GamerData, but they did give him a $19.99 credit to reverse the two charges on his bill.
Maybe he got a bad CSR. Every wireless phone company has them, though in my experience, T-Mobile has the fewest. I was a T-Mobile customer for several years and only switched when I moved and their local coverage was low or non-existent where I live and work. Every time I called them, whether billing related or technical, I always got superb customer service.
Whatever the case is, you should review your phone bills. If you have a routine monthly bill, something like $9.99 would jump out at you immediately, but if your bill varies due to purchases of music, ring tones or services, this could sneak by you unless you reviewed the detail charges. Better yet, one reader at the Consumerist recommended contacting T-Mobile to block any and all third party charges. I had to do that with my wired carrier after being victim to slamming and similar involuntary "services" on my account. It seems the wireless carriers, or one of them at least, has gotten into the same game. Have you seen anything like that on your wireless bill? If so, who is your carrier?