Recomendations: 40 voip lines 10 seat call center.

Hi, what started out as a small two seat call center has become a 10 seat call center. My partner wants 40 voip lines, 30 dialing out on the dialer at a 3-1 ratio. 10 for other inter-office lines. All using the G.729 codec. The dialer will be dialing 6-8 hours Mon-Fri, press "1" marketing. It delivers a 20 second script then allows transfer. It looks like 25-30,000 outbound calls a day.
My Question is: IS Viop the way to go and any recomendations as to which which provider can provide the 40 voip lines econimically? From what I have researched. Most companies are charging per minute rates and some are at 6 second increments and some are per minute. With the amount of dials we are looking at it seems like a lot. Can anyone recommend a flat rate busines provider, not residential. I am trying to fix my monthly cost. What do you think the average monthly bill would be using our configuration.
Also, we would like to have phones with plantronics headsets (S-12) at each station. Do yoou recommend IP phones or using an ATA and regular phones. IF using an ata type, which adapters are reliable? Is this where we could use a x100p adapter in each agent machine and use analog phones? Thanks for the help and recommendations in advance.
Bruce
My Question is: IS Viop the way to go and any recomendations as to which which provider can provide the 40 voip lines econimically? From what I have researched. Most companies are charging per minute rates and some are at 6 second increments and some are per minute. With the amount of dials we are looking at it seems like a lot. Can anyone recommend a flat rate busines provider, not residential. I am trying to fix my monthly cost. What do you think the average monthly bill would be using our configuration.
Also, we would like to have phones with plantronics headsets (S-12) at each station. Do yoou recommend IP phones or using an ATA and regular phones. IF using an ata type, which adapters are reliable? Is this where we could use a x100p adapter in each agent machine and use analog phones? Thanks for the help and recommendations in advance.
Bruce