I've been talking to the WCom MAE folk, and the explained to me that the the VC's between beers are built as ABR, with PCR being twice SCR. Also, the port you lease from them has a non-oversubscription policy, i.e., the sum of all SCR's combined cannot be more than port speed.
From what I can tell, PBNap and Ameritech both build the VC's as UBR, with no over-allocation protection.
In my travels of contacting other providers for peer information, I have run across about 5 (albeit out of about 60 who responded) that said they couldn't turn up new VC's across MAE-East ATM, because they have reached thier subscription allocation, even though thier port is not nearly full. A few had even expressed they wish that it was the ameritech-like UBR model. One person who I spoke to at WCom had said that maybe someday they would allow UBR PVCs, but there was no timeline. What are other people's thoughts on this?