To our surprise we were able to get mobile reception at all bar one of the refuges we stayed at so telephoning ahead to the next days refuge was not a problem.
The larger refuges also usually have pay phones so if in doubt, ask.
To preserve battery charge we kept our mobiles turned off whilst hiking. You may wish to do the same as there is no certainty that you'll be able to charge them at the next refuge you stop at.
Besides remembering to take your charger with you, remember to take a continental mains plug adapter.
We both carried UK pay-as-you-go 'phones and in total spent no more that £20 which included numerous texts back to the UK, a couple of 'phone calls to the UK and the booking of all our accommodation.