Looking for a good SIP client for your Android phone? Sipdroid could be the one you are looking. It is a free SIP client for Android based devices. It can be easily configured to attach to a SIP compliant IPBX. I have tested it with Aastra's MX-ONE and it works just fine. I am able to make incoming as well as outgoing call via the wifi connection to MX-ONE. The voice quality is not bad.
When SIP is so HIP