You need a 3G compatible handset. To know whether your handset is 3G compatible, SMS CHECK to 12345 (toll free).
To activate 3G services SMS ACT3G to 12345 (toll free).
Do dial *147# (toll free) to know about all the plans on offer.
To remain connected seamlessly, go to Network mode in your handset and select the option which provides both 3G & 2G connectivity. This option varies from Handset & Operating Systems.
Eg:In Nokia Symbian OS, the option is "Dual". In Samsung Android OS, the option is "GSM/WCDMA".