Cherries and berries cafe has good speed free wi fi; Address - Vazhuthacaud, carmel towers (2nd or first floor, don't remember; in the same building one floor higher there's another cafe with free wi fi.)

Sarwaa (Sasthamangalam) has an attached cafe with wi fi, but sometimes it doesn't work.

Brewberrys cafe, mangalam lane, sasthamangalam, has good wi-fi. 

 Kerala Travel Boutique provides Highspeed Internet & WiFi access to the traveller. Address: Light House Beach Kovalam, Trivandrum, India,   Phone 04712481028