THe navigation question...that is a very good one. I bought a W760i off eBay and it is just a generic Sony Ericsson, not locked to AT&T, never was. It came preloaded with Google Maps as well as a navigation service and some other apps that are navigation oriented. I did have to get the unlimited internet on it for $15 a month but as for the navigational aspect...well it came with the phone so I don't have to pay extra. It is actually quite fast and I can say it has better satellite reception than a Garmin I have. I tested out our Garmin inside the apartment just because I was excited to have one and wanted to play with it and it could not get satellite reception inside. I also tried out the Google maps inside and it rather quickly pinpointed my location, for fun I did a search for restaurants near me and within maybe 20 seconds tops it found me a list along with directions to each. The other navigation app I have not had a chance to really test out yet, but if the W760i came with these options I'm sure the XPERIA probably would. But this might be because my phone is not AT&T branded, rather it is just Sony Ericsson/Walkman branded.
I actually was just reading about this phone in this month's issue of Men's Health.(my fiancee has a subscription) The excellent navigation options is one of the key points they make about it, as well as the 800x480 color screen, full qwerty keyboard, dual cameras..I could go on. If I had the extra money I would definitely go for this phone, as I have always been a Sony Ericsson fan and this phone promises not to disappoint.