Dial Up Mode means: "No User Graphics, Signatures, and Most Font Changes". It's designed to load quicker and for people who don't want to deal with anything besides text.
It does have to do with dialing with a phone, since people who would use a slow modem use it versus people with a cable modem or DSL wouldn't?
"I wear it for the thousands who have died, believen' that the Lord was on their side. I wear it for another hundred thousand who have died, believen' that we all were on their side." RIP Johnny Cash