i need to run an nec PBX WITH sip trunks on the same physical network as the hosted yealinks, can anyone see any potential problems here.the NEC sip trunks will need to be NATed.

Wow, um ok so I would make sure that they are different subnets and I wouldn't stop there. I would create separate vlans for all three networks (DATA, VOIP, SIP Trunks) and any other things you are putting across the network, as an added side i would implament some kind of QOS or TOS. I also would not rely on a basic low end router and switches to do the work. you want something that does the work with minimal delay to the aggregate throughput.
I would start from the beginning and draw it out and work it out before actually doing the work, It is notebook time. Take many notes.

This topic is two years old. The lack of follow-up posts leads me to believe that everything was squared away since then. Locking topic.