In a relief to millions of mobile phone users, telecom regulator Trai on Friday  said it will take 4-6 weeks to curb the menace of unsolicited calls and SMSes after DoT cleared the '140' number series exclusively for landline phones of telemarketing companies.

"Once we get the number from the DoT, which is expected on (past) Friday, we will be able to implement the series in four to six weeks," Trai Chairman J S Sarma told PTI. DoT has cleared the '140' number series exclusively for landline phones of telemarketing companies to help consumers recognise such calls.

The telecom regulator had earlier asked DoT (Department of Telecommunication) to allocate easily identifiable number series for telemarketing companies in order to put a check on unsolicited calls and SMSes.

While a series beginning with 140 was also allocated to telemarketing firms for calling from mobile phones.

Since the telecom service providers need to make certain changes in their networks, they should be given 4-6 weeks before implementing the scheme. Last year, Trai had come out with recommendations to curb the menace of pesky calls and SMSes.

Since then, many deadlines have been missed for implementing the guidelines in view of the absence of an identified number series. Trai has recommended a maximum fine of Rs 2.5 lakh on telemarketing companies for making unsolicited calls or SMSes to a consumer registered under the national customer preference register -- a modified version of Trai's 'Do Not Call Registry' list.

A call from a landline number can be identified based on a STD code -- the initial digits and then levels (digits following STD codes), which differs from exchange to exchange within a city. It was contended that in case an identifiable series of '140' is used, it would impact the numbering system used at present for allocating new connections.

Adding 3-digit series to landline numbers will take total digits to 13 and to transmit such numbers on telecom networks, especially for caller line identification, BSNL and MTNL need to install new equipment in exchanges.

Subscribers have the option of choosing to be under the 'Fully Blocked' category, which is akin to the 'Do Not Call Registry'. The user can also choose the 'Partially Blocked' category, in which case, they receive SMSes in the categories chosen by them.

Trai has identified seven categories -- banking and financial products, real estate, education, health, consumer goods, automobiles, communication and entertainment, tourism and leisure.