I can't help you with mobile coverage as I used public phones to contact family and only turned my mobile on occasionally to check for messages. That used to be my preferred method but, alas, public phones are becoming more difficult to find. Hopefully you'll never need it but note that the European emergency number is 112.
As for the guide, I made my own from a combination of Miam Miam Dodo and the CSJ guides. For the most part, I prefer to just follow the signs and had no problems doing that on this route. As you're short of time, I think either of these guides would be OK.
Miam Dodo has diagrams of the route, distances, accommodation choices and tells you what services are available along the way. Though in French, the information is presented in such a way that this is not a problem for non-French speakers. For an example of a page from the guide see
http://www.levieuxcrayon.com/MMDDGRARLES/MMDDARLES.html The guides are readily available in France.
The CSJ guide has accommodation choices, distances, information about the villages and services along the way but doesn't have maps of any kind. It's available through their bookshop
http://www.csj.org.uk/acatalog/The_CSJ_Bookshop_Pilgrim_Guides_to_the_Roads_through_France_22.html
One of the outdoor stores in Sydney stocks these guides so you may find that a store near you also stocks them.