... If you can find the owner of that Wifi, please them to secure it, so unauthorized people (like what you did now) can not use their wifi connection...
If they are nice people, they might secure the wifi, but also authorized you to use it... hopefully..

There are a few WiFi Access point router product that have the dial up capability... one of them is APPLE Airport Extreme. You can google for other brand..

read the specification and information or ask about dial up capability, make sure you get what you want.

But, using Dial Up is very slow.. especially if you shared your connection.