I've never met an ISP that sells Racks in a colo that didn't bill transit at 95th percentile (if you chose to use theirs). Are you hosting bare metal, or is your colo providing the physical server?
If you deal with a Datacenter that is just providing you with a Cage + Power + Cooling + Physical Security, you are almost always going to pay for transit @95th percentile.
It's quite common if you ask for a quote for hosting in the UK.
If you ask for a single server you generally get a monthly allowance. For example, one of our servers sits gets 5TB a month on a 100Mbit port. Saturating that 100Mbit port would give me 30TB (and a large overuse bill!).
But if you ask for colo rackspace (1/4,1/2 or full 42U cabinets) then you generally get to choose what drops you get (and what speed), what connectivity and what the 95th percentile billing rate is.
Here's a random example (i've no connection with any person or company in this thread):-
All the colos I've looked at use the 95th percentile. Our bandwidth is 100Mbps but our capacity is 10Mbps. This would be about 26Tb/month. Our contracts are also in the UK so it might be a regional thing.
Single servers tend to use the total usage model. If you're buying space by the rack, you're more likely to use 95th percentile. CDNs often offer both methods and let you sort out which is better.
