In some embodiments, a disclosed method involves receiving, by a source gateway, a call request from a source user terminal for establishing a call with a destination user terminal. The method further involves determining, by a source client proxy of the source gateway, a capability related to a parameter(s) of the source user terminal and a capability related to a parameter(s) of the destination user terminal. Also, the method involves sending, by the source client proxy, a call capability offer to a destination gateway based on the determined capabilities. Additionally, the method involves determining, by a destination client proxy of the destination gateway, whether the destination user terminal can support the call capability offer. Also, the method involves sending, by the destination client proxy, a call initiation message to the destination user terminal, when the destination client proxy determines that the destination user terminal can support the call capability offer.