I just discovered that cingularme.com is not only a mail-to-sms gateway, but also an entire website. It allows Cingular users to customize the gateway service including: creating aliases, blocking certain types of messages, configuring message chunking, and even spam filtering. It also includes helpful tips like replying with "block" from the handset to block future messages from that sender.
I don't know why I never found this previously. I wonder what other neat features they have out there that they've not mentioned.