One of the basic "mangolassian" rules is to always maintain discrete services.
A few examples:
Your PBX provider should never be your SIP provider
Your domain registrar should never host host your web hoster
With web hosting, you typically get "unlimited free" email accounts. (not really free, but paid as part of your hosting contract).
I like to use Office365 for my email.
How do I "unbundle" my email service & use O365 but avoid paying the $5/mo per email account?
Other solutions are welcome!