The short answer to your question would still be a whitepaper in itself. Perhaps you could (at the risk of calling the saleshounds of heck down upon yourself) contact some of the reputable dealers of VOIP systems to coordinate vendor presentations to begin the education process, for yourself and management. Having a vendor rep/SE come along with the reseller to present solutions would balance the sales pitch with real info, and they could answer questions specific to your situation. The sales critters will have all the latest Feature/Advantage/Benefit over POTS speak to wow management. You would have to temper that with reality as it pertains to your business. Our management actually began to outrun us and pulled us along as they caught the fever.
Three years now and we still have the equipment vendor do the dog and pony show when new enhancements or upgrades become available. We have changed resellers a couple of times BTW, but maintained a great relationship with the vendor’s local staff.
Limitations? For us, nothing we could not overcome, mainly we had to ramp up quickly on the system itself.
Benefits? We are a smaller company but spread out internationally – mobile and agile and the system supports us very well.
Advantages? Toll saver for international calls, our mobile staff loves the system, technically more challenging (esp. for our very small staff) but we all love to learn new things.