"#xxxx#" commands: how-to?

As a new E61 user I see a number of commands using the # key that can provide useful info like firmware rev etc (such as "#0000#"😉. My question is simply, how do you use this process? There is no "enter" key so where do you enter this string? In the regular phone dialing process? I entered #0000# and pressed Send and it gave me an error message... Thanks for any enlightenment!