Verizon, AT&T, etc. usually just create a shell for Internet Explorer...their browser uses IE's rendering engine, among other components, but has a revised look and feel and may integrate with other software or services they offer. You may find that some of their browsers will not work properly, if at all, after you install Internet Explorer 7, in which case you would have to choose between IE7 or reverting back to IE6 so you can continue using the ISP's browser until they update it. Since Internet Explorer is at the core it's just a matter of which you would rather use.
John
Hi. I am still learning about pcs and tech stuff, so excuse me if my question seems silly. What is difference in someone using ie7 and using browser software from say, Verizon? It seems the info is the same.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic