Ok so the default behaviour of the app is the sim to which i got the message is the one i can reply from unless i change it with a click(which is nice and easy btw). However this setting overrides the Android default sim settings I set. I can send free messages from my 1 sim but not the other so naturally I set the default s for SMS as the one from which I can send free messages and the message is sent everytime through that one sim only.

So my contention is that if you are overriding the default android sim settings why not go all the way. Give a Sim settings option in the main settings menu of your app and give the following options in that:

1) send from the Sim from which you received the SMS an option which can be enabled or disabled which the default behaviour in your app now.

2) Default sms Sim : Select a Sim and all messages will be sent through that Sim only and add an option to allow Sim change with one click and remember the sim changes that are made with one click while sending messages. The main advantage of this will be I can use the Smart reply through notification itself without even going any further in your app which I have to right now as I have to change the Sim through which theessage is to be sent.

2) Option which can be enabled or disabled to Select any number to which sms can be sent through a pre-selected Sim card only and no change allowed in the Send SMS menu with one click.

This will provide granular control over which Sim to choose for sending SMS and covers most or all of the scenarios.