Having your own plan is a good idea from a credit building standpoint. I've never had a plan under my parents. I got my first phone in 2000 with my own money and own credit. Brad and I joined plans in 2005 when he left Nextell and joined me at US Cellular. I've been with US Cellular since 2001 and have been happy there. We pay a lot each month for a family plan, but it works well for us.
1000 outgoing minutes (calling other US Cellular customers is a free call)
Unlimited incoming minutes (if someone calls us, we don't get charged for using minutes)
Unlimited text/pic/video messaging
5 GB data
Nationwide plan, so no roaming charges
And a bunch of other stuff I can't remember - this is the important stuff...
I believe you can transfer your number to a new carrier nationwide now. I don't think you'd have to change your number anymore when you switch providers.