NEW DELHI: Standing by its decision to charge extra for services like Skype and Viber, telecom major Bharti Airtel today said allowing VoIP calls on mobiles without additional charges was not a tenable business.The company defended its position despite Telecom Minister Ravi Shankar Prasad saying yesterday that the government would look into the matter. He incidentally today tweeted a news report in this regard.Sources at Telecom Regulatory Authority of India also said that they are examining new tariff schemes of Airtel.Stating that it has invest over Rs 140,000 crore in rolling out telecom network over the past years, the firm said it will continue to "charge separately for VoIP services".The VoIP charges are over and above the fee that users pay Airtel for using data services."However, in line with our philosophy of putting our customers above all else, we are committed to making VoIP services extremely affordable and attractive by ensuring adequate minutes for a very small charge on VoIP," Airtel said in a statement. Bharti Airtel has tweaked its mobile internet usage and said that VoIP calls service will not be included in internet schemes that it offers and will be charged at standard data rates of 4 paise per 10 KB on 3G network and 10 paise per 10 KB on 2G network.Based on standard rates, usage of each GB of data for VoIP on 3G network will cost about Rs 4,000 and while the same on 2G network will cost about Rs 10,000.As per estimates, usage of 1 GB data can entail voice calls of about 10 hours, depending on various factors including speed and network strength, while data usage could be much higher for the video calls.Skype and other such apps have gained traction in the recent past mostly because of such services being offered for free and users only pay for the data usage, mostly bundled with the internet package paid for them.The company announced new schemes costing Rs 75 under which a customer can make 200 to 250 minutes long VoIP calls. The scheme will have 75 MB internet usage limit.At this rate, 1GB will cost Rs 1,024 which company otherwise sells for Rs 175 on 2G network and Rs 249 on 3G network.Experts said Airtel's new plan on VoIP is against Net-neutrality principles under which no company should discriminate or pose any kind of restriction on Internet based services.The company said new scheme is "affordable" and said similar VoIP plans will soon be launched for post-paid customers."There would be no other charges in respective of VoIP calls," Airtel said.It said VoIP update is not applicable with immediate effect and the change will be implemented in a phased manner over the next few weeks."In all cases, our customers will proactively be informed about these VoIP charges in advance through the company's standard communication channels like SMS, USSD pop-up, email etc.," the statement said.Pre-paid customers of the company who have purchased mobile internet plans before December 24 can use all services within their pack including VoIP till their packs are consumed or expire.