The best replacement for sccp is sip.

The best alternatives to sccp are rated as following:
★★★★★  sip
★★★★  mgcp
★★★★  sip cisco
★  h.323
★  spcp
★  h323

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

Other search terms related to sccp and their ratings are:
★★★★★ asterisk
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Google Trends

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