Sonic.net

I'll be in the Philippines for two weeks in July. Can I use the Sonic Mobile Communicator while there? Will it cost me more money? I have business voice. Thank you.

My experience is a residential account.

Sonic will not charge you for using it from anywhere.
You can use it to place calls and it will show as the call is placed from your house.
You can use it to take calls as if you were home.
If sonic charges you to call the Philippines from home, then they will charge you too.

The caveat is: only if it works: if the connection is good enough in terms of bandwidth, latency, packet loss, jitter etc (basically MOS)
The sonic voice client does not let you configure much.

I have used it with variable success from France over fiber and over 4G, from the US over satellite connection. It rings ok but the voice quality varies.

Can either of you confirm you are able to make and receive calls SMC with a residential sonic VOIP number overseas over 4G?

I am testing it here at home and it works when I am connected to WiFi, but not when using my Flexiroam international data only Esim connected to AT&T LTE. I have good internet connection, but SMC returns an error when I try to call:

"Cannot make call: A WiFi connection is required for calls."

I will try over Christmas when i will be in Europe and report.

You could try to use another phone as a hotspot and connect to it in wifi.
Get some stats on that connection like bandwidth and latency. I know over hughesnet (geostationary with a massive latency) it only rings while with starlink it works fine.
If you use a decent router os like pfsense, you can simulate latency or packet loss issues to test (traffic shaper/limiters).

One final note is that the provider may be blocking some applications (protocols) so you could test using sonic vpn on the phone over 4g