AOL will open up AIM Phoneline to external developers, to let them create hardware devices and software applications for the internet telephony service.

AOL will give developers access to the AIM Phoneline platform via APIs (application programming interfaces), the web-portal company said yesterday.

AOL, a subsidiary of Time Warner, will make the APIs generally available in this year's fourth quarter, but it will show devices and applications built with the APIs at next week's VON Conference in Boston.

The move is part of a larger trend at AOL and among internet companies in general to enrich their online services with add-ins, applications and devices created by external developers.

Companies such as AOL, Google, Yahoo and Amazon realise they benefit from tapping into the creativity of external developers, be they individuals or corporate programmers.

The resulting applications, often called mashups, extend online services in ways and directions that the internet companies may not have considered or may lack the resources to explore.

For AIM Phoneline, which is the VoIP (voice over IP) service of AOL's AIM instant-messaging service, the hope is that device manufacturers and voice application developers will use the APIs to build new hardware peripherals and software features.

AOL plans to introduce three APIs in Q4 to let developers create ringtones for AIM Phoneline, let cordless phones function with AIM Phoneline and build call management features for the service.