Starting from scratch

I am researching setting up a telephone answering service in the UK. I was under the impression that I would need a switch, many DDi’s and the software to handle different types of calls i.e. call outs, mail order, reception desk etc. together with an platform for integrating message delivery by sms, e-mail, fax etc.

I was interested to read the thread related to using a ‘server’ based telephony rather than ‘switch’ based. Can someone please explain the difference between the two from both a practical and cost perspective?

Thank you for your answers