TechRepublic has a great review of Microsoft OCS. "The verdict: For most organizations, Microsoft's current unified communications product will supplement-not supplant-traditional telephony systems."
OCS has 3 main weaknesses. One is 911.
OCS does not support enhanced 911 location information and not many (if any) third parties provide E911 services for OCS. E911 is critical in a college environment.
OCS does not provide for hunting or conference calling.
Maybe it will be fixed in SP3 or with the next version of OCS.