All the offers I've seen so far are flat rate. Revshare doesn't seem to be common. Do any affiliate networks provide it or is it mainly negtiable only through direct deals?
There are some rev-share deals out there, but it's a lot more difficult to track through a call. There are ways of doing it, but the technology isn't perfect.
Most networks will be able to take a look at your numbers and work out a payout on duration that closely matches a revshare, once they have enough conversion data.
-Mike