ViewRanger is probably the most user friendly "starter" for anyone who already has a mobile phone with a built in GPS.
Basically you don't need a mobile phone signal for the GPS/satnav app to work.
The app is FREE...
OS maps are relatively cheap and I have the whole of the U.K. At 1:50000 that's perfect for me.
There are plenty of FREE maps avaiable to use and download to the phone from the ViewRanger (VR)
http://www.my.viewranger.com web site.
Setting up the handset is simple. Plenty of advice and help from the web site or on the phone help.
I can quickly and simply plan a route using os maps on the my.viewranger.com site and save the route to the phone.
I can then either use my OS UK map or I can "make" a map using one of the free open source maps (cycle map is best) that shows all the roads and most of the lanes simply by highlighting the map squares and download them for off line use on my phone. If I then view and zoom in all the sat image blocks along the route this is stored on the phone memory for 90 days ! FREE... and you can swap between the two on the phone even with no phone signal.
In simple terms the route you made using the free on line mapping is a series of points joined by a line and the software simply fits this to the map you view on your phone and so it follows the roads/lanes shown on the original map you used to plan your route.
Once you learn how to use the toggle to switch between manual point selection and the options of by foot.cycle.vehicle then this fills in the gaps.
It takes a few tries to know how to do it quickly but if I can do it then anyone can..
You can also keep your phone in the top pocket or top of your back pack and set it to record your route when out on a ride.
It takes roughly 10-20 seconds to sync this route to your my.vewranger.com free account so you can keep it to try yourself.
You can download other routes from people you trust have got it right and navigate yourself.
Any no tech savvy person can learn how to use this excellent system quickly.
I got a waterproof handle bar mount for my daughters discarded after upgrade iPhone3 and now iPhone 4. It.s very good value for money, keeps the phone safe and has been under water several times with no issues. I also got the charger that takes power directly from the battery or from your front head lamp supply live feed and earth. Took 5 mins to fit, is power wash safe and keeps the phone fully charged. It is only a single clip to take off the bike and release the power cable. Phone cases available for most phone handsets.
I used to have Memory Map but got pissed with the changing of versions and having to buy all the maps again. ViewRanger does everything you need it to and does it well.
I've had it on the 525 for 5 years now, sun, rain, snow, mud, rocks and it's worked well.
I would suggest that if you have a mobile with a built in GPS (you can use a Bluetooth GPS link) then try the free app with the free maps first..it's free so what have you got to loose?
If you like it then get the OS maps later..
I have even used it for off road routes in Crete with the free maps and sat image and it worked perfectly..