Find out the terms of use for each plan and choose one that best suites your needs. Ask about overtime charges. A stable ISP is constantly upgrading equipment. Ask about connection speeds and capabilities such as V.90. Ask about wait times for connections and complaints about busy signals.
Internet access is a very competitive market today.
Compare the costs and benefits offered by local competitors. Be cautious about FREE service or merchandise offers that require long term commitments. Read the contract before signing. Reputable ISPs offer service contracts that spell out the terms of service and the procedure to follow for termination. Read the contract and ask questions about anything you don't understand.