I think that if he made the deal with you to call if you felt that you were going to cut, he should have been as available as possible at the time whether it be going outside or finding a signal inside the store. He may have tried to do this but wanted to get the shopping done so he could devote his undivided attention to you. However, he did answer the phone and called you back...I'm sure he had good intentions. You are not going to know for sure until you see him and talk about it.

Don't be upset with yourself, you reached out. If there is a next time, he will know that he doesn't have time to finish anything or call you back...you can both learn from this.