This type of billing is quite common in the data world with Internet and MPLS services, so with VoIP/SIP, it is a natural migration.

20% of the phone bill, is the phone bill. Getting rid of the phone bill for a flat rate fee benefits both the SIP Service Provider/Carrier and an enterprise. Whether it is exactly 20% or not is TBD, but everyone does agree a lot of time and costs goes into billing.

As enterprises move to SIP trunking and go through the RFP process to select their SIP trunking service provider(s), they should include a requirement for fixed rate billing. A fixed rate bill is based around peak concurrent calls and/or average number of minutes per month. This type of billing is quite common in the data world with Internet and MPLS services, so with VoIP/SIP, it is a natural migration. Flat rate billing works best in a centralized SIP trunking architecture where all calls come into a couple of data centers.

The advantages of Flat Rate Billing are:

* Predictable--The bill is going to be the same each month, which makes accounting on both sides happy
* Simple--No reams of bills to go through
* Accurate--I have never seen a large company that had a single phone bill that was 100% accurate.
* Cheaper--Both the SIP trunking provider and the enterprise do not have to have dedicate resources creating and validating a bill
* Flexibility--The ability to burst above a fixed number of concurrent for short periods of time.

Will the traditional carriers do this? Yes, when pressed to win business, they will. But an enterprise has to ask! On the consumer side, this is quite common. Comcast, for example, bundles a flat rate fee for their customers. The only thing holding enterprises back is just getting past the traditional paradigm of having a usage based bill or an existing contract.

Unfortunately, this only applies to domestic calls. International calls will continue to have a usage based charge, which is why alternatives like Skype are being deployed in more enterprise environments.