Sony Xperia M Dual : SIM 1 is out of reach when SIM 2 is in use and ViceVersa

[Prafulla]

When I dial from SIM 1, the SIM 2 goes out of coverage area. If I am using SIM 1 and someone calls me on SIM2 it should be shown as call waiting as per standard feature. It is not working in my phone.

[Alexander1]

Xperia M is a 'Dual SIM Dual standby phone'. 

It means that during a call, only the SIM card you have selected to use (the active) is 

available for communications. It is not possible to have two calls simultaneously 
on two different SIM cards. When you use one SIM card to handle calls, the other 
SIM card is disabled automatically.

You can select which SIM card to use, and the selected SIM card will be used for all 
outgoing calls and messages. Data traffic can be set to only run on one of the SIM 
cards. You will receive calls and messages to both SIM cards, however, during a call,
only the active SIM card is available for communications.