I use my Samsung Omnia for Geocaching and it works great. I use two primary apps: RichesseGPS and Google Maps.
RichesseGPS is great because it will import .GPX files from both pocket queries and individual page downloads. It lets you read a static version of the cache info, as well as download the latest info in real time if you want it. Also, it provides the more standard "Bearing & Distance" method for those times when you're out of range of a good data connection.
Google maps is my preferred method, due to the fact that you can walk around guided by sat imagery which makes finding GZ soooo much easier. My main method is as follows: Download a .GPX from a PQ or cache page to my PC. Convert to .KML using Google Earth. Copy both the GPX and KML to my phone's SD card and then run both RichessesGPS (for the descriptions) and Google Maps (to navigate). The beautiful thing is that with a KML file you can have up to 100 caches showing up in Google Maps at once! The latest version of Google Maps also supports downloading info from "My Maps" if you have an account with google. If you have a bookmark set of caches you can simply download the KML file directly from Geocaching.com, upload it to google as a personal (or shared) map and then access it from your smartphone while in the field. Pretty cool. As you can see there are several ways to make it work.
On additional build on my caching method. I recently bought a TomTom for road navigation and I use it to get me close parking to cache sites and then switch over to my phone when I hit the ground. GSAK allows you to convert the same GPX files mentioned above to a TomTom POI file. I even have my setup to alert me as I'm driving around town to nearby caches. The only thing the TomTom isn't really good at is getting you to GZ, especially if its anywhere near a road, as it always tries to snap to the nearest road.
If anybody wants to discuss in more detail, let me know and I'd be glad to walk you through it all and swap tips and tricks.
Paperless caching is the way to go, and IMHO having a smartphone with Google Maps makes it relatively easy.