One of the most important things in life is communication in software development life as well. You will have to communicate with your teammate for many hours each day. There are a few alternatives on market:
- MS Teams
Personally, I like Slack though it is sometimes slow and quite often I don't receive notifications but everything else is pretty fine.
MS Teams is weird - I hate it - some people like it and it's popular anyway so worth a look
Skype is convenient because of its many users worldwide. You don't need any organizations, etc. just write or call anybody. But Skype doesn't manage groups, doesn't provide threads, and doesn't keep history.
You could choose any communication channel but please communicate with each other.