State-owned BSNL on Thursday unveiled an app through which its customers travelling abroad will be able to connect their landlines through mobile and make calls through them without attracting ISD charges.

The Fixed Mobile Telephony service, to be operational from April 2, will however attract monthly charge.

"Under FMT, we have virtually turned fixed lines into mobiles. Now, BSNL customers will be able to seamlessly connect their fixed line phone and mobile phone through a BSNL mobile application," BSNL CMD Anupam Shrivastava said after unveiling a range of modern services.

"After installing the app, customers will be able to use their mobile phone to make calls using fixed line connection from anywhere in the world from April 2 onward," he said.

Under the facility, BSNL customers will be able to use landline phones to make calls using mobile network as well.

"We are working on tariff for this add-on service. It will be fixed charge on monthly basis for both pre-paid and post-paid customers. However, customers will have to pay call rates as per the network they use," Shrivastava said.

If they use landline network, then landline plan rates will apply and if they use mobile network then they will have to pay as per their mobile phone bill plan, he said.

Under this technology, BSNL has plans to introduce SMS facility on landline phones.

"In 2-3 months, BSNL will start providing SMS facility on landline phones. Like calling facility under FMT, people will be able to send and receive SMS on landline phones as well," BSNL CGM Anil Jain said.

BSNL's another facility - fixed mobile convergence - unveiled today, will enable customers to connect up to four devices, mobile and fixed line phones, with each other to send and receive calls, call forwarding etc on any of these devices.

"We have plans to extend FMT service for customers of other mobile network. Then even a customer of other mobile network will be able to avail FMT service provided, he or she has BSNL landline connection," Shrivastava said.

The company also launched pre-paid facility for landline phones.

Talking about mobile network upgradation, BSNL announced that it will install 21,000 additional mobile towers across country apart from 25,000 that it has install under phase 7.

"We have will complete installation of mobile towers under phase 7 in this financial year. Another 21,000 mobile towers will be installed in next financial year with investment of about Rs 2,100 crore. After completion of these projects, BSNL will have about 1,35,000 mobile towers," Shrivastava said.

BSNL is also upgrading its 27,000 telephone exchanges across India with next generation technology from C-DOT which it expects to complete by March 2018.