SIPDroid is a powerful open source SIP VOIP client for your android phone. In short, it enables mobile voip for all android based mobile phones.
When using Sipdroid, it allows you to choose where you will use VoIP, on WLANs only, on 3G, or EDGE networks. Sipdroid primarily supports G.711 A-law.
Sipdroid is a GPL licensed program that allows you to make and receive SIP and make VoIP from your mobile. The app is simple to use, which just requires you to enter your SIP credentials (server, login and password).
Once it is on, you just enter the phone number you’d like or use the phone numbers on your contact list, remembering to enter the country code.
Features of the Acrobits Softphone client include push notifications on incoming calls, bluetooth headset and speaker phone support, call recorder and player, multiple SIP account support, phone contacts integration and a detailed call history.
It is easily set up by the user and offers a logical layout. The Acrobits Softphone app can be downloaded from Android market with WiFi and 3G network capability. Acrobits also supports G.729 codec for better voice quality over 3G networks.
Bria softphone is a SIP-based phone for Android phones that uses a Wi-Fi or 3G connection to make and receive calls. Using Android phone's existing contact list, Bria Android Edition facilitates easy and effective communication management with an intuitive interface that accommodates multiple calls.
Call functionality includes the ability to swap between two calls, merge and split calls and perform attended and unattended transfers.
Bria Android Edition incorporates advanced security settings which allow for secure call signalling and audio encryption. It also contains enhanced audio features including G.711, G.722, GSM, iLBC and an optional G.729 codec for better voice quality over 3G networks.
You can download Bria Softphone app at Android Market.