SRV, which is an abbreviation for Service, is a DNS record, which allows you to use a domain for a specific service different from an Internet site. By setting up a couple of SRV records, you can use the domain with different providers and point it to many servers at a time, each server managing a different service. You'll be able to specify the port number for the connection to each machine, so there won't be any interference. You could also set different priorities and weight for 2 records which are used for the same service, but direct to different servers for redundancy or load balancing. With an SRV record you can employ your domain name or a subdomain under it for a Voice-Over-IP server, for example, and have the actual software running on several machines with different companies. Which one a client of yours is going to use depends on the priority and weight values that you've set.