permit wap ip address to Firewall

[peanutno1]

Hi
I would like to permit an ip address of a wap phone onto our pix 515 firewall, so that the phone can syncronize with our exchange 2003 server using active sync.

I would prefer to do this rather than open up port 80 to the whole world, as our exchange server is sat behind the firewall and we dont have a dmz.

Can someone please tell me how to do this?

thanks!