On my N900, I received an email from a friend whose email address I did not have in Contacts, but I had other information. Unfortuately, there's no functions that allows that -- like merge with contact or add to existing contact. I was also unable to copy and paste it the "old-fashioned" way. Am I missing something?

If you respond to the email, it should add the receiver's email address as an unassigned Contact to your Address Book. At that point, you can merge it with the Contact of your choice.

Tim

You can add the email address as new contact and then go to phonebook and merge the old contact and the newly created contact (in phonebook in the menu "merge contact"). I know this is not an ideal solution as you have an interim step, but it works.