Free calling app between iPhone and BlackBerry?

My friend and I have iPhone 4S and blackberry bold (old model). Does anyone know an app like viber or Skype that would work on both so that we could voice call for free? We tried viber, Skype, tango, but non are available for the blackberry.

Nettalk. Hands down the best.http://appworld.blackberry.com/webstore/content/16942/

Whatsapp? And viber should be available for blackberrys my friend has it.

Viber is in the beta version for Blackberry devices. The current version is called beta version because it doesn't offer voice on Blackberry devices. As the company has been working to create the full version, they have tested it on some devices. More information can be found at http://helpme.viber.com/index.php?/Knowledgebase/Article/View/116/0/blackberry-general-information.

Depending on the Blackberry model, Skype may be available but it looks like you might have to do more than just simply downloading the Skype app on the Blackberry device. Check here and see if this helps http://www.ehow.com/...berry.html and also http://www.skype.com/...lackberry/ (device models listed here).

I found something called Rebtel which is supposed to allow free voice calls between Rebtel app users. You can go to http://www.Rebtel.com and http://alltopstartups.com/2011/01/15/a-new-blackberry-app-allows-free-calling-between-blackberry-and-android-users/ for more information here

I checked out the Nettalk that was suggested and it looks like you have to pay to use it, about 29.95 plus tax per year.

Hope this helps!