Ask HN: Tips to improve payment page?

Any tips to optimize payment page for a freemium site?

So far I have: - highlight the recommended product to buy (eg http://basecamphq.com/signup) - put a security logo to make people comfortable (eg https://www.usertesting.com/ClientSignup.aspx) - include a phone number in case they have questions (eg http://adwords.google.com)

Any others?

Thanks