Side-loading keys (100 pack for $2500?) are different from the mobile device cert ($299/yr) and the Dev Center account ($99/yr) – and they are all unique to each tenant.
- Side-loading keys are way to bypass publishing apps through the public Windows Store and deploy apps to the Windows devices
- Mobile device certs are used to authentically sign the apps
- Windows Dev Center account is specifically used to create a company portal for any apps and for device enrollment
So initially it would be $400 for each tenant. If it’s ever needed to deploy apps through Intune to those Windows devices, then the side-loading keys are necessary.
For ‘how’ the Intune client generally gets installed on a WP8/RT device:
- Get a mobile device signing cert
- Get a Windows Dev Center account and obtain that the “Windows 8 Company Portal App”
- Sign that app with the mobile cert and publish via Intune
- Users (with the Intune account) can then utilize the “Company Apps” built-in function enroll their device and thereby get managed through Intune