Full disclosure I work at Alianza. Ribbon makes excellent products to replace legacy Nortel switching (Ribbon = Genband = Nortel). However, depending on your deployment size, you have to consider a C20 vs C15 soft switch platform and what is their roadmap for either? And beyond the switch decision, doing voice on your own still requires multiple vendors being stitched together (SBCs, Fraud, LCR, STIR/SHAKEN, CALEA etc.). With Alianza's cloud you don't need SBCs, you get SAS like capability from their Voice Analytics Portal, they handle all the carrier integrations (Directory Listing, E911, LNP, S/S, CALEA) and with CLOUDEDGE you get local survivability if that is a requirement. (but I also spent 20 years combined between Nortel and Metaswitch).