How can I assign more than 2 phone numbers to a contact on my iPhone? A large proportion of contacts I have gained over the years have more than two current numbers.

Examples include: home, work, mobile; home, NZ work no., US work  no., Spanish work no; etc

I have only worked out how to add two numbers to particular contact; after that, when you click add there is no other options.

This is crazy, this is 2010, I must be doing something wrong, can you help me out?
I can add as many phone numbers as I want on the iPhone. When you're in edit mode in the contact, there's always a blank line under current phone numbers where you can start typing a new one.

If you click on the label of the number, you can select a label (work, home) and even a custom label if you scroll to the bottom of the label selection list.