Nice! Just a heads up. If you stick with iphone, the new ones will still use the same operating system so there will be no additional learning aside from what you would have left to learn from the iphone 4. The not getting or sending phone calls might be a reception thing. Meaning you may get worse signal at your house than their store. I think the stores have a signal booster on their roof.
I'm sure the guy at the store tried it but you could try doing a soft reset on your phone. Sometimes software can snag and cause weird issues like that. I've seen it before when I used to repair iPhones back at apple 8 years ago or so.
Here are their steps:
Performing a soft reset is pretty simple
Just press and hold both the Sleep/Wake and Home buttons simultaneously for at least 10 seconds, until you see the Apple logo. You can let go of both buttons after the Apple logo appears. Your phone will go through the usual process of starting up. You’ll be back in your home screen.