A DNS "number" that will speed up your internet connection? Give us the link so we can check it out.
DNS translates names into IP numbers. That's it. If a DNS server doesn't have the answer, it queries the next DNS server in line, up the the "root" DNS servers. This takes place in fractions of a second. There are lots of ways to boost DNS performance by the way you set your cache, forwarders, etc. But any ISP worth the name will already have DNS optimized. I'd like to see the link, but I'd give it a 99% chance you're being scammed.
(By the way, guess what happens if you have them host your DNS, and they are unscrupulous? Go to "Yahoo", and they router you to a site they own, but that "looks" like Yahoo; or E-bay, or wherever. You type in a name, THEY route you to the IP address, which may or may not be the real site you're looking for. Log into the fake site with your username and password, and now they own your account. Use a credit card on their fake site, and they have your number. Not to mention... well... I won't mention the rest.)