Ok, I understand. First, on my lockscreen I can see a message of missed call. When I unlock there is a missed call icon on top left on screen. When I swipe down from top, I get a dialogue where I can call back or send sms. Is that what you asked for? This was standard from flash, no mods or xtra app for calls.
HTC One M7 International, TWRP 188.8.131.52, ARHD 91.0, ElementalX 19.5. No other mods.
Nope. He is asking about interruptions.
Normally when you are playing a game or using some app and a call comes, the call screen comes straight through.
But in lollipop, you can set it to show as a notification card which has accept and decline buttons. So that you don't get interrupted while doing something if you don't want to.
I think this is what he's referring to, where you get the ability to reply to a text message from the notification you get from your messaging app.
This is from my S5, BTW, not an HTC.