FritzBox with VoIP handsets

Good morning,

Does anybody have any experience with using VoIP internet telephones (like a SNOM or a Grandstream for example) in an Apple network behind a FritzBox? I am asking as I man considering getting a FritzBox and using a bunch of VoIP phones in it that are laying around here. I would not connect the phones to a SIP provider but just use them as 'normal' phones.

thanks