Much may depend on what service he is being commissioned into. My young man is a Marine and they have a web page for each base he has been at and also one for some level of unit(s) in his chain of command. Some have Facebook pages as well. Not too helpful on keeping in touch but at least I know of some things that are going on in his area. I expect the other services have such things too. I know for sure the Navy has a web page/facebook page for each ship where current activities, promotion pics, etc get posted. Some ships are better doing this than others. Seems like the USS Iwo Jima posts every day, the USS Ashland not so much.
The other thing I would recommend is communicating via Facebook messenger or a similar service. We use it to text at least once a week, sometimes more. Even better we can use it on our cell phones for video conference calls. I don't know how I would have survived without a video call every few weeks, especially for the 2 years he was stationed on Okinawa.