These are the settings we have used to get Skype SIP (Business) working on the IPPBX 2820.

Profile: SKYPE
Register via: WAN2 (we have ethernet presentation)
SIP Local Port: 5070
Domain/Realm: sip.skype.com
Proxy: sip.skype.com
Proxy Port: 5060
Display Name: SKYPE
Account Number/Name: 9xxxxxxxxxxxxx (Your Skype ID)
Authentication ID: 9xxxxxxxxxxxxx (Your Skype ID) + Tick the Box
Password: ************* (Your Skype Password)
Expiry Time: 1 Hour
Trunk Number: 001

We did however have initial problems dialing out, it just disconnected after ringing once or twice no tri tone or anything! embarrasingly this turned out to be a school boy error, Skype SIP exepcts full telephone number even if you set it up as a UK SIP trunk e.g. 0044...

we only use the SIP for UK calls and this is a pain to remember, but you can automate the insertion of the coutry code in the management screens just got to:

IPPBX -> Dial Plan -> Digit Map

Enable: TICK
Prefix number: 0
Mode: Replace
OP Number: 0044
Min Len: 1
Max Len: 15
Route: VoIP1