SRV, which is an abbreviation for Service, is a DNS record, which permits you to employ a domain name for a certain service different from a website. By setting up a couple of SRV records, you will be able to use the domain name with different companies and point it to several servers at the same time, each server handling a separate service. You can specify the port number for the connection to every single machine, so there won't be any interference. You can also set different priorities and weight for two records which are used for the exact same service, but forward to different servers for redundancy or load balancing. By having an SRV record you can employ your domain or a subdomain under it for a Voice-Over-IP server, for instance, and have the actual software running on a number of machines with different companies. Which one a client of yours is going to use depends on the priority and weight values which you have set.