This is what I do to test my free Android app that is integrated with EWS:
Sign-up here:
https://www.microsoft.com/en-gb/smb/products/office-365/
The trial lasts 1 month. Ensure that it is the full business trial -- Do not do a personal trial as it does not have EWS support.
Click "free trial", you'll need to provide a mobile number that can receive a text message token. This is what is used to limit your trials, but you *do not* need to provide any credit card information.
Initially, your outlook/mail options will will be greyed out and there will be a message next to them saying that they are being set-up.
EWS is enabled by default, there is no setup as such required.
Domain: [Leave this blank]
Service URL: https://outlook.office365.com/EWS/Exchange.asmx
[Note: I do have custom domain set-up in my trial account...But this generic service URL works fine...There is a lot of outdated information on what service URL to use.]
[Note: Auto-discover didn't work for me when I tried it, but that could just be limitations of my EWS implementation]
Anyway, I know it is a real pain to develop independent/free software for EWS so I hope this helps someone. I'm pretty sure this is the only way to get a free hosted EWS account [Other than begging your app users to create one!]
Cheers,
Glen