Spree0815,
This is why I try to insist on them doing a 1:1 NAT to start off so we can eliminate the IT staff from the equation right off the bat. Then when they start locking it down the problem is on them to be able to maintain the phones ability to communicate.
Of course even when they do a 1:1 NAT the equipment performing the operation can still cause issues, but you have to start somewhere.
Thanks,
TE