The best replacement for kamailio is asterisk.

The best alternatives to kamailio are rated as following:
★★★★★  asterisk
★★★★★  opensips
★★★  repro
★  openser

Your alternative for kamailio is not listed? Suggest!
Speaking about kamailio, one probably shouldn't forget about freeswitch.

Other search terms related to kamailio and their ratings are:
★★★★★ freeswitch
You have in mind a companion for kamailio and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of kamailio in all years. Click on graph for more.
kamailio
asterisk
opensips