I work with homeless and their phone numbers change. We need to keep all their numbers but add small notes to them. Like busy signal, no voicemail, Old/Wrong Number... stuff like that. Because we deal with so many phone numbers when I was importing the csv list I had to create new fields to accommodate this or it would wind up on the same line. If there was a way to add notes on the contact summary page to quickly reference what's going on with the phone numbers next to the phone number?
One option that wouldn't need any custom code would be to store phone numbers in custom fields instead of in the normal phone fields. Then you can have whatever fields you like for each phone number (phone type, notes, etc). You can set the fieldset to be default open on the contact page, so it would be fairly visible. Otherwise, you'd need to find someone to code this up for you, I'd think.
Circle Interactive had build an extension to support custom fields for Email and Phone, not sure if its been published(can't find under civicrm extension page though). If you want to go through customization would be good to contact them.