The GSM Association (GSMA) has announced an initiative to make instant messaging (IM) on phone handsets work across all carriers together with transparent charging for IM, similar to the way text messaging is currently priced.

Fifteen of the world's phone operators are preparing to roll out IM services in line with the initiative, according to the GSMA. These include Vodafone, T-Mobile, Orange, and Telefonica, which is acquiring UK carrier O2.

IM clients such as Microsoft's Pocket MSN already ship with some smartphones, but follow the model of desktop IM systems. This means there is no specific charge to send and receive messages, but IM traffic eats into the user's data bandwidth allowance, according to GSMA strategy director Nuno Pedro.

"On IP [networks], instant messaging costs you in data traffic. This isn’t transparent pricing, as you don't know how much data is being sent [for each message]," Pedro said.

The GSMA's approach, which it calls Personal IM, will see operators charge on a per-message basis rather than according to the number of bytes sent. Billing models will vary among carriers, but they will typically offer bundles of IMs as part of a tariff, as they currently do with SMS text messages.

"The important point is that only the sender pays with this model – you aren’t paying to receive messages," said Pedro. This will also help to deter spam-over-instant-messaging (Spim), he added.

Interoperability is also a key aim. With some desktop IM systems, it is not possible to send a message to someone on a rival system. With Personal IM, "a Vodafone user will be able to send a message to someone on T-Mobile, and exchange presence information," Pedro said.