Note that your mobile will not have signal and your GPS tracker may not record you as moving in the areas with red dots as signal is weak or non existent. Note that this route is from last year and will change.From Grächen to Zermatt, mobiles work almost everywhere except in a few places where there is no line of sight to the valley bottom. There is no network close to checkpoint 2, although climbing up 50m above the checkpoint can find you a weak signal.
Their is mainly signal up until Monte Moro, but at the checkpoint the signal is weak as you move away from the edge looking down to Macugnaga valley. After Monte Moro, there is no signal until the end of the Mattmark dam in Switzerland.