Why the size of apk so important (~4Mo)? The client contains both ARM5vTE and ARMv7-a binaries. Could I reuse the source code of IMSDroid in my application? Is there a library to develop a custom application? Could I register to any SIP server? Yes. As far as your server is RFC 3261 compliant. How to lower registration 'Expires' value? Is iLBC supported? Yes. But it's only available on ARMv7 (or later)devices. Is AMR supported? Yes. Could I have G.729 codec? G729AB is now supported. Because of licensing issue you have to rebuild the source code. For more information: http://code.google.com/p/imsdroid/wiki/Building_Source#Building_libtinyWRAP.so_with_G729AB Could I have EVRC codec? Could I make and receive calls on the emulator? How to call E.164 (e.g. tel:+33100000000) numbers? How to lower video CPU usage?