WOW thanks magpie, thats a great help, im in a meeting at present (having a break  /cuppa) when you say on 250 im guessing you mean the mitel controller right? 
Thanks again.
Yeah, Not ure why I thought it was a 250 you were referring to!
The set up for a Mitel 3300 is here:
Create a New SIP Device Capability un System Properties / Feature Settings / SIP device capabilities.
Enable the following:
             Replace System based with Device based In-Call Features, 
             Prevent the Use of IP Address 0.0.0.0 in SDP Messages,
             Suppress Use of SDP Inactive Media Streams
             Allow Display Update
             Use P-Asserted Identity Header          
Create a SIP extension under Users & Devices / User and Service Configuration.
Under Service Profile set the device type to 'Generic SIP' & Service Level to 'Full'
Under Service Detail set desired COS, COR & Zone. Set the Sip Device Capabilities previously created.
Under Access and Authentication set the SIP Password - This is the password to configure on the N300.
Under Keys Create a Mulitcall key with the BDN of the extension number on Key 2 set to ring (This allows transfer/conferencing)
Save.