use office telephones that can support upto 3 or 5 calls at a time. users can wear a wireless headphone with numeric keypad to connect to phone.
I have not started my company yet
my friend has started an IT company- he will join me
and if additional management is required I will involve another friend who runs a brick factory, he is also an engineer. I do not know the market potential. I am waiting for your feedback. If I do not get any , I will drop this idea