The Consumer Council has received 143 complaints about mobile data services in the first five months, mostly concerning GPRS and 3G mobile data charges.

The council said today pricing can vary sharply, depending on the means of connection - by WiFi or mobile (GSM/3G) network. WiFi may be free of charge when connected to specified hotspots, but data traffic through a mobile network can be expensive as it is charged based on data volume.

Downloading ordinary multimedia or web pages containing graphic contents can incur high costs when a mobile network is used.

Consumers may not be aware their mobile phones may automatically switch to a mobile network for data traffic when the WiFi signal is weak.

The council strongly advised consumers to pay close attention to the possible charges incurred, and to fully understand the pricing details, terms and conditions before signing any mobile data service contract.

Operators are also urged to provide detailed and clear indications of data content pricing. They should consider alerting users to the amount of data an SMS or email contains.

There were 270 similar complaints about mobile data services for all of  last year, 108 in 2006 and 55 in 2005.