Sure, you can totally set up a button to make phone calls in your app. For Android, you'll need to set permissions in your manifest and use intents to start the call. It's a bit tricky, but it's doable.
From my experience, you'll need to add the CALL_PHONE permission and handle the intent to dial the number. If you’re unsure about a number that's been calling, using something like who called me can help identify it. It’s saved me a few times from unknown numbers.
