IPOffice is a great pick. Good support. Tried and tested.
Asterisk is also a good pick.
Depending your the needs, Vmail, call center, paging, teleworkers, etc., Asterisk gives a big bang for the buck.
VMPro could easily provide centralized voicemail for both sites in this scenario.
What is the cabling like at both sites? IPOffice allows digital phones working on single pair. If the backbone at either site is a nightmare, digital phones are a great.
If cabling was not an issue, the network infrastucture was sound, I would pick Asterisk due to the increase in features you get for the money.
If money is not an issue. If cabling is not the best. If a poor decision can cost you your job, I would pick IPOffice.