I have been testing various VoIP apps for Android and finally settled on Grandstream Wave. After disabling the SIP ALG helper on my router, I am able to make calls over my home Internet connection between two Android phones, a Galaxy S4 running Android 5.0.1 and a Galaxy S6 running Android 7.0. 22.214.171.124 Warp is installed on the S6 but I disabled it while I got GS Wave working.
When I enabled 126.96.36.199 Warp on the S6, GS Wave was able to authenticate with the SIP server but could not initiate a call to the S4 (“No response”). However, the S4 was able to initiative a fully functional call to the S6. I have an OpenVPN server on AWS - if I bring up OpenVPN on the S6, I have no issues with calls initiated either from the S4 or the S6, so tunneling the traffic through my home router and ISP should not be a problem.
Before dig into IP traces, has anyone else seen this issue? I have been running 188.8.131.52 Warp on the S6 for almost a month and have not experienced any other issues. I see no issues based on cloudflare-dns.com/help.