I would say US Cellular
Verizon currently has the best rated cell phone service in the US.
Att. Att has the fastest broadband network and covers 97% of all Americans.
You can view a cell phone directory at places like US Search, Spokeo, the National Cellular Directory, and Akiba. The National Cellular Directory would be your best bet. It is also free.
of course...
No, you do NOT have to purchase a replacement phone from US Cellular. I have included a link below to an online cell phone store that sells US Cellular cell phones. Hope this helps.
Talk to your phone-company they will do it for you for a small fee.
yes
Password lock
it depends on the phone you want to buy. your phone must be capatible with US Cellulars technology. This information can generally be found on the carriers website. US Cellular uses CDMA, so your phone needs to support CDMA. A GSM phone will not work on US Cellulars network.
No
when at&t, sprint,verizon etc... get a new phone, us. cellular gets it 6 months to year later. i think us cellular doesnt want to pay for a phone till it comes down in cost. i have been a costumer of us cellular my self for many years and i have been asking that same question over and over.