I was a single M. for five years, and dated during that time (remarried now, and my husband is a great step-dad!). Here are three things that might help:
(1) Let them know that due to cell-phone etiquette, you will not be answering your phone at certain times. Give them the whole list: during shows, during meetings, when you are having time with friends, during church, etc. Basically, get the message across that it is rude to disturb programs, meetings, church, etc. with phone calls, as well as rude to interrupt conversations with other people to take calls. It doesn't matter whether you're on a date or doing one of these other things, it will be clear that there will be times when it is rude to answer your phone. THEN FOLLOW THROUGH! (They can leave messages.) When they are with you, ignore some calls, and point out why you are doing this.
(2) Set up a system for knowing when a call is an emergency or very urgent. Define "emergency" and "urgent" so you don't get calls about not being able to find the toothpaste or brotherly quarrels. Our definition involved "When there's blood beyond needing a bandaid, illness that needs attention immediately (e.g. not a mildly sore throat), or special situations that cannot wait until I'm home. For my kids, they know that if they will call twice in a row (within a couple of minutes) I will excuse myself, and call them back ASAP. They are to leave a message on the first call letting me know the situation, so that I don't panic.
(3) Call to check in every once in awhile. YOU choose the timing (go in the ladies room on a date), and this is when they can tell you non-urgent things. They will come to expect this and can learn to wait.
Remember, just because he calls, doesn't mean that you have to answer. Presumably, you have left him in capable hands. He has no right to feel betrayed or ignored if you have explained that you are simply going to be following proper etiquette from now on and will check on him every couple of hours. Don't train him to feel entitled to your immediate attention when you're apart. This will be as good for HIM as it is for you.
I commend you for keeping your dating above the children's radar. I did the same, and although it was hard at times, it kept my children from having a parade of people come in and out of their lives.
Diane