In reply to Jon&anne-marie:
If you have line of sight down towards Aviemore/A9 corridor you'll get a signal with all the major phone networks.
In Sneachda as you drop down into the corrie reception is patchier depending on a/ LOS and b/ your network. You get a good signal on O2/Vodafone/Orange by the rescue box in Sneachda.
Lochan - generally a good signal (I'm with O2) all the way in until you drop into where the lochan is. The signal returns as you go higher (again LOS to A9 corridor). Hope this helps.