How to convert a city mobile into a virtual one?

Question

Telephony

The company has its own city mobile number, which it has been using for several years from the Tele2 operator.
Now the task arose to connect a cloud PBX to Zadarma in order to create internal lines.
I really want not to lose the number, but the Zadarma system requires you to connect a virtual number for incoming calls, otherwise you need to contact a provider that supports call forwarding via the SIP protocol.
How can (and is it possible) to bind this number as a virtual one?

Answer 1

Option 1: Buy an FXO-SIP gateway and forward calls for free.
Option 2: Try to transfer the number to a megaphone, a megaphone provides a multiphone for free, which is SIP.