Sonim XP3 Enduro is the most ruggedized Tri-band GSM/GPRS phone you can find. This phone is waterproof, impact resistant, and is impervious to sand, dust, mud and micro particles.
IP-57 and Mil Spec 810F certified, hardened rubber bumpers, a higher volume speaker, Bluetooth, and can operate in extreme temperatures from about 4º F to 176º F.
Only thing missing is GPS features which would have made it a perfect outdoors companion.
$600 via SonimXp3.com