Thanks for the advice all, really appreciate it, especially for a "guy off the street".
Our system is the original MXE - I dont think it is a II and I know it isnt a III - thats what the vendor want to upgrade to.
We have ISDN, SIP is a bit difficult where we are, and in 1 to 3 year we are relocating to a new site - 250+ people, two factories, warehouse the lot - totally greenfields - we may not even stay Mitel.
So Im trying to figure out how to keep the world going for a year or two, not have the global HQ phone system reliant on a PATA / IDE drive and not spend money in private manufacturing - oh and deliver everything that's wanted now. Fun times.
Have heard I can swap our the PATA drive in an emergency, our local provider appears to be conservative, if I was using our Indonesian or Vietnam providers I don't think this would be considered so "difficult" or "risky".
So I think my plan is that I will get the controller virtualized, leave the MXE as the ISDN gateway, possibly even upgrade it to a minimal MXE III even if its "just for insurance". Then when the new site is up, SIP it, hook the SIP to the virtual and decommission the MXE.
Just need to figure out the timing for OS upgrades, we are 4 our 5 people effectively looking after a 1000 - resources are very stretched and I need to keep Call Center going.
My understanding if we upgrade the controller to v8 we have to do Call Center at the same time but we can leave the clients on the old software and catch up with their end device upgrade and training later. The business wants me to continue a MiCollab trial, even if its 7.X whilst all this is happening then catch up to 8 when all done. Again fun times.
Like you guys I have been very confused by the 52XX incompatibility and challenged our vendor twice, for ref here is what they said: "...the 52xx series handsets do not work as they cannot be linked via the MiTai proprietary signalling. This was only a capability introduced in the 53xx series phones...".
Im disappointed, they are a workhorse, the 100Mb is a problem but Im getting great deals on the 2nd market - probably as everyone is trying to get rid of them.
Thanks again for the comments / advice. Really appreciate it. I might post some other questions if thats ok - its a challenge to not having been in this work for so long to come back to 6 challenges in one month.
One last thing, from your guys opinion and experience, if you were going greenfields for 250+ staff - would you stay Mitel? Half my meetings seem to be our vendor apologies how "confusing" the software / options / licensing / roles are.
Note we have recently installed Mitel controllers in New Zealand, Indonesia, Vietnam, Singapore and about to do China - so moving aware from Mitel for the HQ would be a big step.