When my husband was overseas last year, he used to record himself and emailed it to me so the kids could see him and hear him talk
A lot of people I knew got their partners to tape themselves reading a storybook so that it could be played for the kids when they went to bed which is also a great idea.
The kids need to know that their dad or mum is thinking of them and a recording is something that can be played back whenever needed, so a great idea in my books!