I pay [*] for a business DSL line (static IP, 20:1 contention, etc). I've faxed my provider 3 times to try and get them to delegate rDNS to me and they've done nothing. I've now given up. SPF is a more complete solution to the problem that rDNS based blocking is trying to solve.
FWIW, unless you have a /27 or larger, you are unlikely to get an ISP to delegate the rDNS to your server. However, you may have better luck asking the ISP to change the reverse IP directly, so that the forward and reverse DNS correspond to what you'd like them to be. I know that my ISP will do that for fixed IP accounts (SpeakEasy).
HTH
John
