sip_session: rename variable

darcs-hash:20090324115505-b2873-e8bea67aa4f1e101e4e2a8d7ff2089c2a1abeebb
sip_session: add ringtones

darcs-hash:20090324115530-b2873-89bea76bf06682ca94938836a3724c5d9f3591c3