VOIP Support Mobile IM help

Hi,

I am developing Im which has to support VOIP between users, as openfire supports SIP plugin and asterisk plugin, I am thinking that I would be able to support VOIP feature, however I wish to know for SIP can I use SIP API JSR 180, which is provided in SIP enabled mobile device to implement this service. If yes then which plugin would be helpfull, in real time the SIP plugin or the Asterisk plugin. Or do i use MJSIP library for the sip support.

I am using Openfire 3.6.2, and AsteriskWin32 to dvelop this IM.

Thank you in advance for your reply.