The problem is it does not work with semicolon delimited phone numbers in iOS. Do you know if gvconnect url scheme will support bulk call (multiple numbers at the same time? For single number I can have skype installed (Free), I tested the skype: url scheme and that works fine. (Something like this is possible with skype but skype does not support conferencing in IOS. an installed VOIP in iPhone will listen to the protocol and place conference call to all three numbers. So I was looking for an SDK or App that can accept call request from other apps. But developing a VOIP app from ground up is not worth the time (and I dont know Obective-C either). I need to make VOIP calls (and conference call with multiple phones) from my iphone application. I have a custom iPhone application written with C# and MonoTouch. Is there any VOIP app for iPhone/iPad that can accept call request from another custom iPhone application?