I'm going to take a different viewpoint to the others....perhaps because I'm old enough to remember when people would go on holidays and we'd be out of contact with them for a few weeks. I remember when my hubby had to go overseas for 3 weeks and I was absolutely thrilled (and satisfied) to receive one call from him. I think it's terrific when a person isn't so addicted to his phone that they can actually turn it off for a week. So, the fact that he's turning off his phone isn't alarming to me at all. Having said that, I think it would be nice to agree to a call on Christmas Day.
My main questions pertain to where he's going, why and with whom? Unless he's going to stay with his family who happen to be out of town, I'd be finding this trip away very odd.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.