If you have a Dual sim mobile, you might come across various problems while making a call. This is due to the nature in which the Dual sim technology works. You may first see all types of Dual sim phones to understand it better.
One such problem, that you may encounter is ‘Check Operator services’, that doesn’t allow you to make outgoing calls. This may be because you are using line 1 for calling where you should be using line 2, or vice versa.
To solve this problem (for all dual sim phones of Micromax, Karbonn, iBall, Celkon etc), all you have to do is make a line switch. For most phones, there will be a line switch setting under (Sim 1 or Sim 2) Call settings. Just change the line and your problem should be solved and you should be able to make outgoing calls.
All you are doing here is using the correct line with the correct sim. If you are trying to make a call using sim 1 while line 2 is in use, you will get the mentioned error or vice versa.
If you have a Nokia dual sim mobile, you can switch the line by just holding down the # key for some time.
Note: Although this is the most common reason (irrespective of network, Airtel, Vodafone etc) to get the mentioned error, there might be other reasons as well. For example, if you are call barring enabled for outgoing calls, you might get similar error)