Remember, you don't know what they're going through. Try calling at a time of day that makes sense. It's direct and synchronous. Ask them how they are and what'

Remember, you don't know what they're going through. Try calling at a time of day that makes sense. It's direct and synchronous. Ask them how they are and what's new in their life. Try and find time to meetup. Life gets really busy for people and they might see the commitment it takes as something they just don't have time for right now. Or maybe you've grown apart. You can always ask them if everything is alright between you both.