I recently purchased a new TashiCell prepaid SIM and noticed that the Caller Ring Back Tone (CRBT) feature was automatically turned on, and so callers were hearing a tune until the call was answered. I didn't really ask for this service, so I inquired at TashiCell's Customer Service about it.
Apparently the company is offering a free month or so of CRBT for new subscribers, but - and here is the catch - they start charging Nu. 1/day after the trial period ends, unless you ask to disable the service. Well, I don't really like this business practice. While it makes perfect sense to offer a free trial period for the CRBT service, it is not OK to start charging for something that a customer did not specifically ask for. I also wouldn't be surprised if many folks out there are not aware of the daily CRBT fee.
Anyway, if you want to cancel CRBT, you can use SMS. Send the message dreg to 9797, and you're done.