Bug reports, patchs are welcomed !
The prefered method is to send to linphone-developers mailing list (you must subscribe before).
Alternatively you send an email to simon dot morlat at linphone dot org .
You can also help the project with donations: use the paypal link below or donate webcams, it is can useful to improve video support.
There is a project page on savannah.gnu.org, on which you can retrieve and browse cvs source code, get development releases, submit patches.