The only two mobile networks which operate on the island are O2 and Vodafone. Although the island is relatively flat the coverage for these two networks is rather broken and intermittent in certain locations. I confirm though, both have excellent recpetions in Kilmoluaig at Struthan Cottage.
If you use another network, and you need to have mobile contact, you will need to ensure your phone is unlocked and then buy a SIM card for your phone from either O2 or Vodafone before you arrive on the island and fit it for the duration of your stay. Phone ‘top ups’ can be purchased at the Co-op in Scarinish.