ASP based or Hosted Call centers

Hello All,

I am helping a group open up a 24 seater call center and I am looking to start with an ASP initially. I need first hand opinions on this issue. Anyone out there who have used an ASP especially the PD and outbound please respond with frank opinions. I already know of Telephony@Work and genesys plus does concerto have an ASP ? What about MCI?

Thanks in advance.