I can't vouch for their SIP service, but I've had Granite as a provider for POTS lines. They are a reseller and my experience with them was less than stellar.
LoPath
Maintain HiPath 4000 V5 & V6, OpenScape Xpert V4 & V6, OpenScape Xpressions V7, OpenScape Contact Center V8, OpenScape Voice V9