1) User friendly interface, user should all SIP settings just once and each time user can just make a call. user also should be able to receive calls and answer them as well.
2) Mobile Dialer supports SIP for signalling.
3) Mobile Dialer supports G729, G711 codec for sending audio data.
4) Mobile Dialer can run behind NAT or on private IP.
5) client can hear remaining balance by listening to IVR
6) Mobile Dialer runs on application layer so it supports GPRS, WiFi,3G network and Bluetooth for internet connectivity.
7) This software will run on the phone having Symbian platform.
The more compatible phones is the better quality.
8) Able to use Mobile Dialer with any kind of Soft switch which support SIP
9) Dialer should be built with Symbian C++. Unless you have J2ME version then we can try a demo.