At first, the HT-502 worked like a charm. It was simple to set up, the two ports worked in tandem without a hitch, and all seemed right with the world.
About 2 weeks into ownership, suddenly one or both ports started losing SIP registration and failing to reacquire it: i.e., phone service would suddenly terminate, at times mid-call. The various VOIP forums had a number of complaints of similar behavior. Corrective actions that seem to have been successful for other users failed for me. Upgrading the firmware from the stable version (from 2010) to a new beta version made no change at all. Grandstream support has not responded to a ticket.
Additionally, quality of voice service began deteriorating. Echo cancellation stopped canceling echos. High frequencies became horribly distorted and clipped. And calls started breaking up, as if I were using AT&T Wireless service when not standing directly beneath a cell tower.
I could have lived with loss of registration -- painfully, but power-on resets aren't that difficult -- except that the last time the circuits dropped, the whole unit failed. It will not power on; its LEDs are blind; I am without phone service on two lines.
Alas, Grandstream seems not to offer a warranty, and I'm 2 weeks beyond the point where Amazon will accept a return. I aim to replace the unit, but am unwilling to take the risk with another Grandstream. A six-week lifespan for a phone switch is unacceptable.Even if it's just this unit that's a lemon, support for it is abominable.