Keypad requires periodic sequential scanning and if you want to put the scanning microcontroller to sleep something else has to scan it (keypad) instead ..
One option is to use dedicated keypad IC (with an interrupt) such as the MM74C922 ..
Here is it's detailed description: https://www.elexp.com/tips/74C922.pdf
I'm not sure what you mean by pressing the 1*# keys. Do you need a special sequence?
You can add a few "OR" diodes to you keyboard matrix, so when you press any key it sends an interrupt signal to the microcontroller. Here is an Atmel example:
"AVR240: 4x4 Keypad - Wake-up on Keypress" http://www.atmel.com/dyn/resources/prod_documents/doc1232.pdf
Simple solution is to wake up the CPU for short time every 1 or 2 seconds with timer interrupt
To scan the keys if any key pressed
And if not, to send the CPU to sleep