Implement VOIP in iphone and ipad.

Question

Hi,

Does anybody is aware of implementing VOIP feature in iphone and ipad.

The Things for which i need clarity is,

1. By using which third party library/protocol can i implement this feature? or is der any in built classed available in objective c which i can make use of??

2. Is there any Apple store accepted iphone application which uses VOIP iplementation?? If so where can i get implementation details of it.

3. This is a generic question. Can we use any third party's in our iphone application or do we need to get any special permission from Apple reg the usage of third party's used.

Please let me know if needed more details reg this.

Thanks , Santhana