Since the APN settings are carrier specific you need to get back to your carrier for what these settings are.
Let me share my story anyway. I had Sprint and Virgin Mobile and suffered the issue you noted. Data would bow out for days and could barely make a call or text. Turns out Sprint had decommissioned a tower in my area and that was that. I had to move to another carrier. A few phones later and a little trip to learn more about that carrier's APN settings and it's all better.
First off, I apologise if this question has been asked 100 times before, I did a search through the forums and found nothing.
So, a few days ago I found I was unable to make or receive any phone calls. Calling out would just time out, and people calling would be put straight to voicemail.
Now, I have found that going into Settings > More Networks > Mobile Networks, and changing it to "2g (voice calls and SMS only)" has 'fixed' the issue, however I now cannot use mobile internet because of it.
Any ideas on a proper solution?