Im at RAF Halton now and my phone works fine, so does everyone elses on my flight, not heard of anyone having a problem. Just bear in mind that you'll only be allowed to use it after you have been dismissed in the evening and even then only in the barrack block. You'll get dismissed about 8-9 in the first week, about 6-7 in the seccond week. Phones are to be off (as are lights!) by 2300.
All the best with your training, you'll absolutely love it, its VERY hard work but great fun!