Our phone system needs replacing.

Current set-up

All devices connect via SIP over IPv4.
The secretary number makes both the Snom360 and Siemens DECT ring:

exten = s,n,Dial(SIP/secretariat&SIP/dect_sec,15)

The following features are now in place:

Proposed set-up

We would like to get rid of the server and go for a hosted solution. This would then allow us to get rid of the 4 KPN ISDN lines.
Since we actively use IPv6, any hosted solution should ideally be accessible via IPv6.
The SwissVoice phones should be replaced by something new and better. Since we have good experience with SNOM, this might be good option?
SNOM also has IPv6 support, and they seem to have all the devices that we need: fixed phones, DECT phones, conference phones.

The following features are required:

In addition, the following features are wanted:

Phones should have an easy to use history button, and it should be able to redial numbers from the history (no weird stuff with missing leading zeroes etc).

We are open for any suggestions and ideas regarding this set-up.