We’re using standard analog phones with Grandstream Handytone 286 DTAs, and everything works beautifully. Only issue (which was resolved by simply turning call waiting off) was that when we were on a phone call and somebody called our extension and call waiting was invoked, it was very loud and you could hear a faint ringing in the background. As soon as the other caller hit voicemail, the phone call became very garbled and sometimes disconnected. I don’t believe it’s a bandwidth issue because be have 3 - 4 people on the phones simultaneously an any one time, this only happens during call waiting.
Not too much of an issue now since we turned it off, but just curious why it might be doing this. Maybe not even an issue with Asterisk, but rather the DTAs.