Sending text messages to mobile phones via websites might soon cost money. Two major Dutch mobile phone operators have blocked incoming text messages sent via several websites and instant messaging software.

KPN Mobile and Dutchtone want to see cash. The operators, which together serve about 6.2 million of the roughly 11 million Dutch mobile phone users, say they have to allocate space on their network to carry the large volume of messages sent to their customers via the internet, but don't get a penny for doing so.

Both operators have blocked incoming messages from South Africa's M-Cell, which operates the popular SMS website, powers the SMS functionality in ICQ and is the parent of mobile operator MTN (Mobile Telephone Networks). Dutchtone has also put a stop on text messages coming from Swisscom and 02, which was formerly BT Cellnet.

"Over 80 percent of the incoming international SMS traffic comes from MTN, Swisscom and BT Cellnet," said Kiki van Erven for Dutchtone, a subsidiary of Orange. "It doesn't make us any money and it takes up network capacity that we would rather use to allow our customers to make phone calls."

"The SMS messages are given to us for delivery. It takes network capacity to do that, so it costs us money. There is hardly any SMS traffic from our network to MTN's network," said KPN Mobile spokeswoman Caroline Ubachs.

KPN and Dutchtone aren't the only ones throwing up SMS blockades. It's an international problem, says Pia Rogers for Swisscom.

"Other operators have also blocked SMS messages coming from Swisscom. They don't make any money for distributing international SMS messages. Also, we distribute bulk SMS for advertisers, which has led to objections," she said.

But some don't buy this argument. Airborn handles web SMS services and doesn't understand the operators.

"There is significant revenue generated around the world based on our service. We are stimulating multiple millions of dollars in revenue. As a result of our messages people send messages and call," said Ari Kahn, co-founder of Airborn.

Sending a text message from a website or from ICQ is free, but there's a charge for sending a message from a mobile phone. SMS is seen as a 'cash cow' — that is, it provides a steady profit — for mobile operators and the cost for SMS hasn't dropped in line with the price of mobile voice calls.