There are 2 mobile network companies in Mauritius:
Emtel and Cellplus
Sim cards from any of those 2 are readily available in most large supermarkets et.c.
While Cellplus is known to have better coverage, some people argue that Emtel's service is better....
This has been discussed before - please follow this link:
http://www.info-mauritius.com/forum/fto ... ight=emtel
Hope this helps