Cellphone data content - ringtones, wallpapers, MMSes - are expensive, and many people have responded to an advert thinking they were making a one-off purchase, but later finding themselves locked in to a subscription service.
Both the Advertising Standards Authority and the Wireless Application Service Providers Association ( Waspa) - which regulates the content providers - have had their hands full dealing with complaints about this devious practice.
One tab
They can be especially expensive if your service provider somehow fails to bill you for your usage for eight months, then discovers its mistake and bills you for eight months' worth of ringtones and things - on a single bill.
That's exactly what happened to about 5 000 Altech Autopage subscribers on the MTN network.
Their May bills were whacked with all these accumulated charges - in some cases small amounts, and in others, hundreds of rands' worth.
June Parkes of Durban usually pays between R90 and R135 a month for cellphone usage.
But last month she received an SMS stating: "Please be advised of MTN late billing for data usage since October 2006 due on next account. E-mail queries to "
June's alleged accumulated data usage was more than R600.
She insists she didn't receive any such data.
When she did ask Autopage's customer services department for answers, she was told that the "back billing" was all MTN's doing.
Ant Brookes of Waspa said the organisation had fielded about two dozen similar complaints and was currently spending hours examining itemised bills regarding disputed charges.
"We're a very small organisation, so we're swamped by this," he said.
"The biggest problem is the bills don't say what the charges are for, so each one takes a lot of investigation."
So what happened, exactly?
Autopage Cellular MD Janet Featherstone said because of an Autopage "system error", the data records which MTN had sent to the company had not been picked up and billed to their customers - for eight months.
When they picked up the mistake, she says, they decided to pass on the costs to their subscribers, because Autopage had had to pay MTN for the services, and the subscribers had benefited from the services.
"We understand that our customers will be out of pocket this month," Featherstone said, "and we sincerely apologise for billing eight months of content charges in one month."
She acknowledged that some of the affected subscribers denied using the data services at all, and she suggested that they get in touch with the content providers directly, or lodge a complaint with Waspa.
Featherstone said Autopage would willingly provide subscribers with detailed information about which content provider generated the charges, and what content was provided.
To my mind, it would have been fairer to the affected customers to send them a letter in advance, explaining what had gone wrong, advising them of how to query the charges, and offering payment options to those who couldn't afford to pay for eight months' worth of data charges in one go.
When questioned on this, Autopage spokesperson Robyn Botha said "the credit controllers staggered payments where requested by the client".