Hi Valve90210,
No idea if this has been resolved yet, but thought I'd add a couple of ideas -
From troubleshooting our own office VOIP service over the last year this sounds like it's an issue being caused by a routing problem on the VOIP provider's network; Lync in this case.
Your IT guys should be able to trace the SIP session through your phone system when you're trying to call home which should give some clues as to where the call's being dropped.
If Lync can't establish a call/session to your phone number, the phone system should be getting some sort of error message back from their connection to Lync which will often help indicate whether the problem lies in your phone system, with PN or perhaps with Lync - giving enough ammunition to get a fault raised with the provider and the problem sorted.
It's not entirely uncommon for the odd routing problem to creep into networks, especially where numbers are ported around between providers or networks; and on the positive issues can usually be sorted pretty swiftly once identified.
Hope this maybe helps
Tim
