Welcome to the Apple Support Communities. I understand you're having some trouble with phone calls, and being one of the fundamentals of having a smart phone, I can certainly understand your concern. There's a great article for phone call issues you should check out: If you can't make or receive calls on your iPhone - Apple Support
Be sure to follow every suggested step, in the order they're recommended, and make note of any changes (or lack thereof). Let me know those results and I'll keep working with you if that article doesn't straighten it out.