If I have a bad telephone line will I have bad internet?
Ghost Of Christmas Past
If that's the only line into your house, it's likely changing providers won't increase your internet speed. You'll need to check your Vodaphone agreement to see whether you have to pay line rental. Generally the owner of the local loop (the wires that connect you to the rest of the world) charge whatever it's used for.
It will Suck.
You need to get a connection from a certified internet provider.