Hmmm, I might be able to at least shorten the solutions list by two entries. I made my solution a Bugzilla entry since it really is easy to fix, and my solution would solve one of the other issues on the list as well. My proposal is to permit free-form text in phone numbers. This also solves the proposed solution of permitting extra field types (you can enter the text in the number rather than the field type).

For example, you would be able to enter a US phone number as:

+1 (555) 123-4567

rather than the much less readable:

+15551234567

and you can even add things like:

+1 (555) 123-4567 (Old number)
+1 (555) 123-4568 (Current number)
+1 (555) 123-4569 (Parents)

Or whatever other comment you would like.

Having extra text in numbers seems to work well in all places I have tried it (several phones, SyncML web-sites and Outlook), but extra field-type names are not portable. Several other apps and phones already permit free-form text entry. The N900 has no problems with free-form text in phone numbers once it is there (i.e. imported from a vCard for instance), but the text-entry field prohibits all but numbers to be entered.

Have a look at bug 8297 for more details (and please do vote for it).