When considering what to use to communicate with others we will use different tools. These may include:
We need to ask why we are communicating, and who we are communicating with, before we can decide how we should communicate. Perhaps we need to consider the tool being fit for the purpose:

Ask yourself whether you need to interact with one, or more parties. Ask if you want to keep a record of the interaction. Is the reason for interaction important and is it necessary to interrupt the other person (as you don’t know what they are busy with). If you need information do you need it now, or can it wait until tomorrow or this evening.
Do you expect others to immediately respond to your interactions? How often do you check your emails, WhatsApp messages, SMSs and social media services (Facebook, Instagram, Pinterest and others)?
Like you, everyone else is busy too. Respect this and use a tool that is appropriate:
Each of us use the tools in our own way. There is no standard guide that everyone sticks to when using communication tools.