Verizon Wireless will begin offering free Skype calls and instant messages to nine of its Android and BlackBerry devices beginning Thursday as part of an exclusive deal with the mobile VoIP provider.

Users of the service will be able to place free, unlimited Skype-to-Skype calls and IMs, as well as low-cost calls to international wired lines and cell phones. Using the service will not count against their voice minutes or data plan with Verizon.

“This was something that seemed improbable at best to the industry who wondered why on earth a carrier would want to partner with Skype,” said Skype General Manager Russ Shaw.

John Harrobin, senior vice president of digital media and marketing for Verizon, said that the offering was targeted at Verizon customers who frequently place international calls, such as business subscribers and foreign exchange students.

Harrobin also said Verizon and Skype were working to expand the free service to new platforms and capabilities, such as video.

Verizon is also working to expand the Skype offering beyond BlackBerry and Android devices, but declined to be more specific.

The free Skype app will route calls over Verizon’s circuit-switched voice network instead of VoIP, which is traditionally used to handle voice calls. Harrobin says Verizon decided to go with its voice network over VoIP because of quality concerns with calls routed over IP.

“That’s what the network was designed for – voice. Data networks are not designed for voice,” he said.

Though Skype is available as an app for several different mobile platforms, the company said the capabilities of its Verizon app will remain exclusive to the carrier. “It will be the best Skype experience out there,” Shaw said.

Beginning Thursday, the app will be available through download to nine BlackBerry and Android devices including the Motorola Devour, which will also come out on Thursday.