I remember upgrading Ubuntu 5.04 to 5.10 with dial-up. It took about 700MB distributed along a few weekends (at least here in Brazil, phone calls pay a flat rate on weekends, otherwise it is a small amount/minute - I don't remember how much, as I now use my landline only for ADSL). I also downloaded quite a few Linux ISOs and a good amount of music with dial-up.