New iPhone. Got signal yesterday, but not today.

I picked up an iPhone yesterday and it's working great. I'm just having one small problem. Yesterday, it showed several bars for signal strength all over my city. At my house, the signal was perfect.

All of a sudden today I get no bars everywhere I go. The phone still works and I can make calls but the signal strength in the top left corner is as flat as a pancake.

I'm not sure what's going on. Anyone have any thoughts?

A simple restart seems to have solved the issue!