Customers may soon get a respite from pesky calls and SMSes as the DoT has cleared the ''140' number series exclusively for landline phones of telemarketing companies to help consumers recognise such calls.

"DoT has cleared various issues, including that of security, to provide telemarketers the 140 number series for landline phones, which will be issued in a week," a senior DoT official said.

Telecom regulator TRAI  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 allocated to mobile services earlier, a separate identifiable number series will now be allocated for landline numbers.

Last December, TRAI had come out with recommendations, 'The Telecom Commercial Communications Customer Preference Regulations, 2010' 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.

DoT had pointed out various technical, billing and security concerns in issuing a number series for landline services.

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.

"All issues relating to security have also been cleared," the official said.