VoIP calls are possible and besides Android we can do as if estuviramos doing from a fixed telephone, which is interesting because of the high rates of mobile phones. The main idea is to make the mobile telephone operating system Android might look like a conventional telephone with a telephone number and achieve a cost fixed 0, for which will be important to have a centralized PBX with which it is possible IP calls and in addition to the advantage of using a single telephone number to be the place where we can find and without exercising any cost. But speaking of prices, if we use the VoIP DDI will have to pay around 7 euros per month and if our telephone call from abroad to spend fixed phones, the cost to be about 2 cents euros and if we call phones cost phones be 8 euro cents but without paying the cost of establishing a call that normally costs about 15 euro cents.
But above all, the main and essential to make the calls if necessary we can make VoIP calls with our mobile telephone and that some companies are prohibited from making such calls to Simyo such can not be done by contract and Movistar filters the traffic of VoIP calls, but at least in Spain, MÁSmovil permit and then be necessary to have a softphone to run the call on the mobile phone, a softphone to make calls at your home or office and also can be an IP telephone and a VoIP supplier to have our phone number.
The softphone for mobile can be Sipdroid is free and although it has CDEC G.729 integrates with the PBX or Keyyo PBXes, which provides services voIP with G729 codec and also is free. Lastly is configured with two outgoing lines and a number of input, ie configure 3 extensions, two and one fixed MOBILE.