Strange, the link works just fine here. :s
To quote from the wiki article...
[color=#0000CC]"PLANS You may select any of your plans to give another web ID access to. You may also allow access to all of your plans if you'd like. Having access to a plan basically means that you can add services such as users, domains, databases, and mailing lists to that plan, up to the amount that plan provides. It does not allow ending, upgrading, or downgrading the plan. You'd need to have billing privileges to do that. Basically, if you want to allow somebody to add their own new services through our web panel, you need to give them access to a plan!"[/color]
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