said by Wampler :I just asked my IT person at work and she said Grandstream is one of the big ones for equipment. They look pretty good and seem to have a lot of different gear for different needs, why don't you like them? and what do you use? Do you use the Obi ones?
I don't dislike Grandstream; their equipment is reliable, reasonably well supported and inexpensive. If I wanted to connect 20 legacy phones to a new IP PBX, I'd probably choose Grandstream.
However, their low-end boxes basically connect one phone to one provider, or two phones, each to its own account at the same or different providers. Given that you stated a requirement of two providers and use of existing phone "equipment", which implied that you have more than one phone, I recommended Obihai to provide features that I thought would be useful.
I personally avoid ATAs and spend a little more for decent IP phones. However, I do own an OBi110, which is used to interface IP phones to a pseudo-POTS line (triple play from ISP). Also have an SPA3102, connecting the system to a real POTS line, and have an old SPA2102 for the alarm system and occasional faxing.