Cisco Phones and an Algo Alerter. Is this right?

Hi All
Hear me out on this one Im trying to figure out if an external Phone provider is doing things the right way.

Cisco 504g Phones, Needed in a warehouse, so I suggested to the Phone provider to add an Algo SIP Alerter 8180 to the system so that the client can hear the phone ring over the machinery in the warehouse. The phone provider claims the Algo will need an ATA device as the Cisco phones won’t work with the Algo, and the ATA needs to be configured with a phone number which would incur a monthly fee. I’m not sure if the ATA needs a phone number, I would presume the ATA would be provisioned on an Extension on the VOIP system rather than needing an actual phone number.

Any Clues?