The best replacement for 3cx is asterisk.

The best alternatives to 3cx are rated as following:
★★★★★  asterisk
★★★  switchvox
★★★  trixbox
★★  freeswitch
★★  shoretel
★★  elastix
★★  airdroid
★  mitel
★  bria
★  digium
★  freepbx
★  x-lite
★  snom one
★  sipdroid
★  csipsimple
  zoiper
  x lite
  xlite
  sipxecs
  pbxnsip
  axon
  4cx

Your alternative for 3cx is not listed? Suggest!
Speaking about 3cx, one probably shouldn't forget about spa3102.

Other search terms related to 3cx and their ratings are:
★★★★★ spa3102
★★★★ skype connect
You have in mind a companion for 3cx and it is not yet here? Propose!



Google Trends

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3cx
asterisk
switchvox