ABTO Software's VoIP SIP SDK allows quick VoIP softphone app development. Also you can use it when you need to add VoIP features to your software. VoIP SIP SDK for Android provides: *Android 2.x/4.x support *SIP and RTP support *DTMF support; *STUN support; *SIP Registrar (SIP server) support *video and voice calls; *hold call support; *IM text chat. Sample app is available at https://play.google.com/store/apps/details?id=org.abtollc.softphone and https://play.google.com/store/apps/details?id=org.abtollc.videosoftphone Also the sample app: *can be rebranded; *works with most SIP servers, including ABTO SIP Server and Asterisk; *can work without SIP server in intranet; *communicates great with most sip clients including softphones based on VoIP SIP SDK for Windows. Available codecs: *G.711-ALaw/muLaw *G.729 *Speex *Theora *GSM *H.263 *H.264