MCI is set to launch a VoIP-over-DSL service it says could save small offices money.

Slated to be announced this week at NetWorld+Interop, MCI Advantage over DSL is designed to let businesses with up to 60 users at one location consolidate their voice traffic onto a one symmetric DSL connection to reduce costs vs. traditional telephone services.

The offering works by moving analog or native IP voice traffic through an integrated access device, over an MCI DSL connection to the Internet, where it's passed to the public switched telephone network. The service includes unlimited local and long-distance voice service.

Local exchange carriers have pioneered VoIP-over-DSL services, but MCI is out in front of interexchange carriers such as AT&T and Sprint. Sprint says it is trialing such a service in Las Vegas.

MCI's offering supports up to 15 simultaneous calls, though offices of 40 to 60 people can sign up for it on an oversubscribed basis, figuring not everyone is on the phone at once. On a monthly basis, MCI charges a flat fee based on line speed, plus $40 per simultaneous call.

The service could cost up to $850 per month for a 768K bit/sec DSL. Using MCI Advantage over a dedicated T-1 for the same office would cost about $1,500 per month.

Some users might be willing to pay extra for a T-1 because meantime-to-repair guarantees from carriers are typically stronger with T-1s than with DSL, says Brian Washburn, an analyst at Current Analysis. Users can expect a T-1 to be repaired within four hours of an outage, with DSL meantime-to-repair usually within 24 hours. "Users need to be aware that they may be sacrificing cost for a slower meantime-to-repair guarantee," he says.

The service is available in the 31 metropolitan markets where MCI offers its own DSL service. The carrier says it will expand VoIP over DSL with Covad Communications in the third quarter. Covad's DSL network reaches 235 metropolitan markets across the U.S.