Strong is relative. If you plan to drop it 10 times a day then no it is not "strong." I have dropped the phone twice since I bought the phone and it took the abuse. However, I don't like the slippery feel so I bought a silicone cover which works well.
There are fees associated if you cancel your plan or change the phone number associated with the equipment within a short waiting period. As far as warranty goes, I do not believe amazon officers a warranty just the manufacturers warranty on the equipment. A lot of times verizon will off you the ability to buy on a monthly plan assurrion insurance. Assurrion has many loop holes as well such as the 150 deductible. For that you can buy a new phone from Amazon.
I have pre paid cellular phone service with Verizon wireless for $45/month and 500MB of data. Verizon does 4G LTE pre paid now. No contracts with your own phone. A coworker told me Straight Talk does 4G also with 3GBP of data/month. I haven't checked for myself. I received this phone without a Sims card. Verizon gave me one free. You may have to get one as well.