Have fun, but be careful. Crime rises when unemployment is up, and French unemployment is up. Big crowds attract pickpockets, but locals say they’ve gotten more brazen.
Beware of online scammers, who are also more brazen. If a friend is hunting for a place to stay, the Committe de Tourisme d’Affairs, the mayor’s office and other accredited bodies have an official list of realtors who have passed intense scrutiny (cannes-rentals-certification.com) or do an online search for Cannes Rentals Certification. (Variety has used one of these companies for years.)
So be careful, but don’t be paranoid. Only a tiny percentage of folks in Cannes are dangerous. Most of the festgoers are benign (they’re a little crazy, but that’s what makes the fest fun).

Telephone repair:
GSM Expert
5 Rue Marechal Joffre
+33 4 93 39 33 84
(English spoken? Not guaranteed.)

New Services Serge
10 Rue Jean Jaures
+33 4 93 38 05 72

Cannes Retouches Service
11 Bis Rue Helene
+33 93 39 40 20

Buro Copy
6 Rue Notre-Dame
+33 4 93 39 19 49

Apple products:
7 Rue Teisseire
+33 4 92 18 92 00