I’ve found White Pages to be a very nice, freemium app. It’s the free part that I am most interested in, though. As its name implies, it gives you white pages telephone listings, and yellow pages as well. It has a good interface, and it seems to have everything the dead tree phonebook would have. That alone is quite useful, and the data-entry part in the app interface is much easier than trying to use a web page not optimized for mobile.
But the real value-add comes from the integration. In one click you can map and navigate, or add to your contacts. I find that very convenient. A nice bonus is one-click emailing of the address.
Where the freemium part comes in is tying the lookup functionality to Caller ID. Standard land-line Caller ID doesn’t carry over to the cell world–you just get the number (unless the number matches one of your contacts, of course). White Pages bridges that gap, by intercepting the incoming number, and looking up the white pages listing, if there is one. I haven’t really tried this, it comes at a price, and I don’t really need it. I also tend to avoid unnecessary “TSR-ish” things on my phone where possible, especially when they could interfere with the most fundamental phone functions–I don’t want my phone hanging or crashing when I’m trying to take an incoming call.