The Scottish government has reviewed mobile phone coverage in Scotland. Their report can be found here http://www.scotland.gov.uk/Publications/2013/09/6141/1 The most interesting page is here, giving the findings. http://www.scotland.gov.uk/Publications/2013/09/6141/5 Figure 11 on that page shows that Shetland is by no means the worst for 2g Not Spots (22.9% with Argyll & Bute having 38.9% of its area where there is no phone signal). Shetland is the worst for 3g. It is not available in 77.4% of the islands. Only Argyll & Bute and Highland come close.