In reply to JonCork:
wifes an ER nurse, she reckons as long as its not advanced frostbite (dead flesh, black, blistered etc) that a few times a day try this:
2 buckets of water. 1 bath temperature, the other cold from the tap.
stick the affected hand in the warm for 3 mins, then the cold for 1 min.
repeat 3 or 4 times, ending with the warm water.
make sure you dry the affected area well and keep the hand warm when you go out.
ive had this with both big and 1 other toes, and tho the feeling never fully returned to one big toe it helped overall.
good luck, and be careful in the future as you may be now more susceptible to further damage.
let us know how you get on.