OK, I just tried to merge Cloud telephony into Web-based VoIP, and it did not work.  The reason is that the intros in both of those articles did not correctly define the concepts.  
 Cloud telephony is a subset of Cloud communications; it means third-party, off-site VoIP services in general.  This includes both web-based and non-web-based VoIP (it could just integrate with conventional telephones as a PBX replacement).
 Web-based VoIP simply uses a web page running a multimedia applet or whatever instead of dedicated non-web VoIP software

I propose merging Cloud telephony into Cloud communications instead; they are both very short and weak and there is substantial overlap.  I tagged both of those articles.

There is no section in Voice over IP into which to merge Web-based VoIP, since it defines a class of client software; though I did add an awkward link from the "Protocols" section.  Clients are described at Comparison of VoIP software.  Web-based software is included there but not necessarily marked as such.  That's another potential merge target, but I don't have any problem leaving web-based VoIP as its own article for a while and letting it grow.  It may be handy to just be able to link there from several other articles. I removed the merge tag from Web-based VoIP for now, but feel free to rekindle the debate if you see fit.