RED 15Wi Setup Query - VOIP and subnets

Hi Guys,

I am setting up a new remote site office and will be provisioning a RED 15Wi at the location. We have an SG230 here at 'Head Office' which we've had for a year now - all working OK on this end!

I understand the basic 'plug and play' config and principals of the RED Device and Environment but have a query in regards to our VOIP phones. Our VOIP phones have a static IP programmed into them already (192.168.1.x/24) and here at Head Office I have a number of segregated vLANS for network traffic (10.0.10.x /24, 10.0.11.x/24. 10.0.12.x/24 etc) and the 192.168.1.x subnet purely being for VOIP.

The new site is only 4 people and the new PC's for them have been setup and joined to our domain, but I would like to have it authenticate back to here via the tunnel on their own subnet similar to how the ones here are setup ie 10.0.20.x/24 and I want my VOIP phones to come back through the RED Device back to our phone system here on the same 192.168.1.x/24 subnet we use here (Phone system is on 192.168.1.200) - if you get my drift? As mentioned, the VOIP phones are already pre-programmed on that subnet and we only have 10 of them so there is no chance of address conflicts ;)

A few years back, and the reason why I got the VOIP handsets in the first place, is that we did have a small site office and I did setup a tunnel from that site back to here using our old Cisco Firewall here at Head Office and an old Snapgear Firewall onsite 'back in the day' and it worked beautifully. I'd like to do that again with my SG230 and the RED 15wi. 

Wifi will also be used on the device, one being our own Corporate access and I am thinking of turning on a wireless guest that would go straight to the internet if possible.

Any tips or advice would be greatly appreciated ;)