I'm using a cheap Android chinaphone, have loaded OsmAnd on it. App is free, unless you want to upgrade to the paid version. Maps are opensource and thus free as well, and can be downloaded via wifi.
However, no smartphone is as robust, weatherproof and as convenient to use as a good GPS.
Sent from my Android chinaphone, please excuse the spelling
'11 Yamaha YBR125G (cheap and very cheerful
'12 Zongshen Fly / Motorstar MSX200-II (biggest-fun-to-dollar ratio of any bike I've owned)
'03 Honda VFR800 (sold)
'06 Husky TE610 (gone)