Hi, push notifications are already supported by kamailio by means of t_suspend/t_continue functions (http://www.kamailio.org/docs/modules/devel/modules/tmx.html#tmx.f.t_suspend) and tsilo module (http://www.kamailio.org/docs/modules/devel/modules/tsilo.html). You can watch this video (https://youtu.be/4XIrR9bwUkM) and read the related presentation (http://www.kamailio.org/events/2015-KamailioWorld/Day2/20-Federico.Cabiddu-K...) to see how put all the pieces together.