We sometimes deploy 3cx in mpls, even if its not that much larger. its not so easy as sometimes, some issues we have :
- if its an operator dependant mpls, there can be some restrictions in terms of sip trunk (for exemple 2 trunks of this operator on their mpls not possible at the same time!)
- if the old ipbx is not well managed by a someone who really know what is he doing...you need to be clear at first that you will not manage their old ipbx!
- you need to manage well dhcp server. For exemple if you move only few site, phones need to be reset by someonelocal and dchp of this local site only has to be modified to send phone to the new vlan properly. As I am not an expert in managin this kind of big mpls, I can't do it if the IT of the client is not good.
As you see, for me, oftently the problem is that they want to change because there is not enough knowledge on the client side anymore...it doesn't help the transition!
If you do others way I will be happy to recieve some advice, please share
