The quick answer is “Yes, most of the time”.
The longer answer is “It depends when and where you are”.
Verizon and AT&T are working well right now as I write this.  Problem day is always the Tuesday morning of Marburger.  Verizon caught on several years ago that there are a lot of people out here in Round Top, and did something so that for four weeks a year the thousands of people out shopping for antiques were able to make a phone call. Fingers crossed that this year AT&T has done a similar fix.
If you cannot get a call through, keep trying, or try sending a text message.  Often a text will get through while a voice call will not.  If the call can wait, try calling after about 5pm – don’t ask me why, but it seems easier to get calls through in the evening.

MAPSandART has a cell phone booster in their booth at Blue Hills at Round Top.  We are in Barn A.  Stop by if you are having trouble and we can try to get your call to go through!