Hi,
You also of course have the option of purchasing a commercial license and remain on-prem.
The features of the hosted SMB version are available on the list shared earlier. In general you will not be losing anything - you can set-up an instance and check. This version is free, inclusive of hosting.
You cannot do a backup and import to the hosted version, you will need to setup as new. Please note that you will most probably need an SBC to connect your current phones to it, and your SIP provider must be one of the ones included as an option for SMB, not all are compatible. A new 5 digit extension range will be assigned to you by the system.
Best,
KS.