Anyone ever used this?

Our company is thinking about getting a T-1 line to use for these VOIP phones.

Just wondering what experiences were with it.

Also, if you have, have you ever used it with a PBX system?

I have high hopes for this, considering that our T-1 + vonage system would be $1700 a month for phone and data charges vs our current $6000 a month we pay for phone service.