I use a windows phone and run Memory Map. I have an HTC phone, it will play your MP3s, films, take piccys, access the web, make calls, it has an FM radio, will run Memory Map and it runs TomTom too.
All in one handy, phone sized package.
However, as you probably know, these phones aren’t as tough as say a garmin and I wouldn’t strap my phone to the bars for continuous guidance.
I guess that if you know roughly where you’re going, but want to stop and check occassionally during the ride, then a phone running MM will be fine, just keep it in a pocket or your back pack and dig it out for a look at where you are, as and when.
If you’re looking for something you want to look at while riding, in order to follow a route, then something like the Garmin Edge is fine. I’ve a 305 Edge. Once I’ve laid in a route/course, its simple, no brains riding, just follow the line on the display.
Solo.