come here to ask the same time. From what I see so far it seems only Huawei Mate 9 for android. Some googling also shows that Volte seem to rely on telco specific implementation as well, maybe they havent put much effort into porting to other phones as well since it probably require them to specifically code for phone models.

if u can live with slower speed since it caps at 5Mbps, then yes worth. Note that any video streaming listed in their VideoOnz will be capped at 1.2Mbps as they force u to stream at 480p, but u can use VPN to bypass that if u have one.

as far as Damansara area, which part? damansara isn't exactly small. I'm using P78 as well, and in my experience, outdoor area is good, mostly 4G and some area has 4G+( not that it matters since our speed is still capped anyways ). Indoor it differs a lot and depends of the area has repeater installed or not. OneUtama is very good, and signal improvement seem to be massively improved in the past year. iSetan area use to have 0 reception, and suddenly, H+ full bar, then now 4G+. The other places I cant say for sure, but as far as I know, uMobile uses 2100hz for 3G and 2600hz for 4G, both are low penetration frequency( then again, havent update myself with latest changes so this could be wrong ), so u can expect indoor performance to sometimes drop a lot.