The BSNL has announced revision of ‘prepaid’ 3G/2G Annual Data Plans that allows customers to migrate to other prepaid mobile plans without losing data benefits, from August 1.Earlier, customers subscribed to Annual Data Plans were not allowed to change their plans - like Mithram, Per Second and Per Minute. The latest tariff revision allows plan migration for all BSNL prepaid customers who have subscribed the Annual Data Plans. BSNL offers four different Annual Data Plan Vouchers (Data Card Plan-96, Annual Data Plan-1251, Annual Data Plan-2299 and Annual Data Plan-3299) under the prepaid 3G/2G segment.The base tariff - Per Minute Tariff - is same for all the four Annual Data Plans. Only the plan voucher and freebies differ. Under the latest rationalisation of tariff, Annual Data Plan customers are also allowed to use any of the Live Plan Vouchers.If a customer gets migrated to another plan, he/she will continue to receive the data plan bundle every month up to 12 months, but the validity will be as per the new plan.