To protect mobile phone consumers from the frequent and sudden changes in tariff plans of access providers, the Telecom Regulatory Authority of India on Wednesday mandated a minimum validity period of six months for the plans offered by them from the date of enrolment of the subscriber.

The mandate, which comes in the form of an amendment to the Telecom Tariff Order 1999, protects the subscribers from any increase in tariffs during the six-month period and also allows the service providers to reduce tariffs any time.

Under the plan, a subscriber shall now be free to choose any other plan even during the six months period while the service providers are also mandated to accept and implement all such requests for change immediately or from the start of the next billing cycle, TRAI said in a statement.

"The new provisions will ensure that the service is available to the subscribers for the chosen price level at least for six months and also make their migration from one plan to another more transparent and consumer-friendly," it said.

TRAI has decided not to change the existing cap of 25 tariff plans on offer.

"The new provisions would curb the practice of the operators offering new regular tariffs, tariff plans and withdrawing or revising it suddenly, upsetting the basic considerations on which the subscriber has exercised his choice for the tariff," TRAI said.

TRAI had issued a consultation paper on limiting the number of tariff plans by the access providers in March.