Mobile phone reception on Coll
There are currently (Jan 2021) two operational mobile phone masts on Coll. A third is in the pipeline having been granted planning permission (Oct 2020).
EE operate from both masts (soon to be all three).
Vodafone and O2 only operate from the mast on the hill in the middle of Coll (Cnocan na Ban).
All three of EE's masts have/will have battery and diesel/LPG generator backup. Vodafone and O2 only have short-life battery backup.
However, there's a lot more to this complicated story. Most mobile reception on the east coast of Coll, from Sorisdale down the wilderness coast to Arinagour village and beyond to Hyne, receive mobile signals from Ardnamurchan and Mull - not as many believe, from Coll's community-owned mast, Cnocan na Ban.
From the airport around to the the west coast and as far north as Windy Gap is served by Cnocan na Ban mast. Many places also receive from Tiree.
Sadly, there are still places without a signal, or it's too week (mainly a Vodafone thing), particularly on beaches and in hollows.
You may read O2 as being very similar to Vodafone.
A third mast, about to be erected on Windy Gap, will serve the east end of Coll from Gallanach to Sorisdale but only for those on EE. The mast is being installed as part of a government strategy for 4G emergency services coverage.
On the face of it, it may appear EE offers the best option. However, their Arinagour mast (and probably* their soon-to-be-erected mast at Windy Gap) only transmit on 1800 MHz, frequencies which may only be available to EE contract phones - and not on Pay-As-You-Go deals (this may have changed by now) - and not available to other phone suppliers that piggy-back off EE towers (see MVNOs link).
Coll's central Cnocan na Ban mast transmits on 800MHz for all three operators and 1800MHz for EE.
The situation is dynamic with improvements all the time, so please keep an eye on this page. I'll do my best to update as soon as I get any information but real information, as opposed to social-media hearsay and/or wishful thinking, is sometimes difficult to come by. The mobile phone network is quite secret and, for example, technical details of the two operating masts on Coll is close to impossible to find on the internet.
* Still unsure on this one, only time will tell. 800MHz signals are more penetrative and travel further then 1800MHz signals but 800MHz has less bandwidth/speed. Since the Windy Gap transmitter has to cover all the East end of Coll it may well use both frequencies to cover the distance. Most EE remote, west-coast masts operate on Band 3 (1800MHz).
MVNOs: a guide to virtual networks (which network your mobile phone works on)
Where's my mobile signal coming from: Android App here (There's no Apple equivalent app)
If you're considering going 4G for your broadband by installing an external aerial, suggested readings, I hope it'll help.
List of operating frequencies used by UK's four mobile operators - here