I believe the game will run off Dial Up, but will take time in downloading updates and any map and area updates that occur between instances and towns etc.
It could all depend on your overall system specs though as to whether it will run any good. Don't forget, if your system specs are no good, no matter the Internet Connection, it will be very poor, and running a poor system with Dial Up will be even worse.
Post a little more info on your system and you will get further and better answers.
