Its tough to remember how huge Rebtel is for an internet service, considering how dominant Skype is in the VOIP space. The Stockholm-based service just hit more than 17 million users, growing at 650 000 users a month. Customers are logging in over 1 billion minutes a year, with projections for an $85 million dollar run rate for 2012. That’s not bad. The company tells us now they have released an iPad app that provides free Rebtel to Rebtel user calls, as well as calls to any phone for rates that can be up to 60% cheaper than Skype’s.

“Along with the gift of increased screen real-estate, the iPad has given us the ability to rethink the Rebtel user experience while balancing the benefits of the platform with the same sense of familiarity we strive for across all our products,” says Andreas Bernstrom, CEO at Rebtel.

Rebtel looks pretty hot on the iPad, and makes good use of the platform. More and more people are using tablet devices for their VOIP services, so the move makes sense. According to a recent study from Nielsen, 77 percent of tablet owners stated they use their tablet devices for tasks they previously relied on their computer for.

Rebtel’s model is differentiated from Skype’s. While the company also has a desktop client, with Rebtel, dialing another phone that has Rebtel installed is free. And the company is playing the numbers game, if Rebtel is not installed on the phone of the person being called, you get VOIP rates that are either competitive, or up to 60% cheaper than Skype. It’s designed to be your go-to calling app for cheeper rates.

The iPad app can be downloaded here.