Trouble getting IP Phone to work

[Henry]

- I'm running PF.
- I have an IP Phone here that uses the 3com NBX phone system.
- Residential cable broadband connection with dynamic IP.

When I use binat, the phone works 100%.

When I use NAT with redirects to forward, the phone works partially.
Some features don't work at all, and the others work sometimes.

To further test, I had NAT on, redirect all traffic to the $phone and
passed all traffic and it still doesn't work 100%.

Example:
----------------------
nat on $ext_if from !($ext_if) -> ($ext_if:0)
rdr on $ext_if proto {tcp udp icmp} from any to ($ext_if) -> $phone
block log all
pass log all keep state
----------------------

I see nothing being blocked, everything is passing and all incoming
traffic should be going to the phone. So I'm kind of stumped. Any
ideas?