The best replacement for xmpp is sip.

The best alternatives to xmpp are rated as following:
★★★★★  sip
★★★★  irc
★★★  jabber
★★★  amqp
★★  mqtt
★★  jms
★★  socket.io
★  webrtc
★  websockets
★  signalr
★  comet
★  smpp
★  gcm
  socket io

Your alternative for xmpp is not listed? Suggest!
Speaking about xmpp, one probably shouldn't forget about google voice.

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



Google Trends

Scale is based on the average worldwide traffic of xmpp in all years. Click on graph for more.
xmpp
sip
irc