Comments in their forums mention "radio points", presumably provided at intervals by the officials to give emergency communications. Here's an account of the stream rescue, from OMM:

For anyone who wants to know, we tried to cross a "stream" (unfortunately can't get the name as my map washed away a little bit...) was about half way across when my feet went from under me. apparently i went somewhere around 200yards downstream, washed up on an island, within a couple of mins of which phil and tim moseyed up from checking out the ford(?) lower down. spotted me, looked for rach, got my dad and sis leggin it down the hill instead having sent rach for help at the nearest radio point and luckily finding a group of walkers (neglected by the media i notice - inexperienced walkers out on the hill at the same time, also requiring MR/emergency services in some cases), one of whom had a phone.
A while later (no idea of time) after having wrapped me up in several layers, a tent, space blanket etc, and constructed 2 tents on our little island we heard the whistle of the mountain rescue team and soon after the roar of the helicopter which whisked us away (and half our kit downstream but nevermind!!).

So it sounds like they used the mobile phone of a passer by, but there was an alternative in place. Also she sounds to have been in fairly good shape and may not have actually needed rescuing. (She's already booked up for next year.) Even ignoring the passers by, there sound to have been a lot of people on the mountain who could help.