We also use them, and they are EXCELLENT.
Telebroad's service is excellent & their prices are too, (we use them in our company).
But one of the main cause for having issues with VOIP phone service is the modem & router not being configured correctly, so you have to make sure it's done the right way by a real professional.
Also, if you have many phone lines at one location it's best to have a separate internet line for it, and not to use the same as for the computers.
And if Fios in available in your area, use that for the phones, instead of cable internet service, because cable - even at a high speed - is not running on a consistent straight speed which at times might cause voice quality issues, vs Fios which always runs at the same speed level.