MUMBAI- Telecom operator Mahanagar Telephone Nigam on Thursday said it would launch mobile TV next month, for which it is carrying out field trials at present. "We have tied up with a technology partner, who is carrying out the field trials. We would provide 21 channels," MTNL Executive Director J Gopal told PTI . The firm, on Thursday, launched 'Express alert', a value-added service for its Dolphin and Trump mobile subscribers. Subscribing to ‘Express alert’ would give MTNL customers updates on astrology, cricket scores, news and stocks. Going ahead, MTNL would launch one value-added service every month to increase its revenue earnings. Telecom operators are witnessing a fall in their revenues because tariff is declining. So, they are launching value-added services that are popular among subscribers. For the value-added services, telecom operators have tied up with a technology partners and they share the revenues. The lion's share of the earnings goes to the operator.