How to work in background
This is the developer, IOS4 does not support UDP running in the background.
So we still use the push notification service to receive the incoming calls in the background. With the selection of our public push server or your local private push server (if your sip server cant be reached by our public push server), you should have no problem to receive the calls when the app is in the background.
You can download the private push server vmware image from our website. Just make sure you have set up the virtual servers interface to bridge mode, so your isip can talk with the virtual server.
The IOS4 support gives you the possibility of doing VOIP calls in the background and do other work in foreground. You can also go back and continue VOIP calls after the VOIP call is interrupted by cell calls.
vnetcorp about
iSip -VOIP Sip Phone