atcomsystems.ca/forum Forums TDM Business Telephone Systems Avaya - Lucent Telephones & Systems IP Office and VOIP

To have a chance of functioning as you describe, you need the equivalent of Tie Trunks between IPO and hosted vendor's "PBX". If the hosted vendor supports QSIG, that is the most realistic. If hosted vendor doesn't support trunks, upgrading IPO won't help. As mdaniel says, best results would come from an all-IPOffice solution.
Mike