I decided to get an Iphone 6 from Consumer Cellular. I was using them for my Android phone. They also offer a “bring your own Phone” plan where they send you an SIM. They use the AT&T network. Rates start at $10 a month, and they sell call minutes and data plans separately. Check their website for Iphone models and prices.
I agree that the built-in Apple Support is all you really need. It lets you adjust the volume, change the program, and start the Live Listen which lets your Iphone be a remote microphone. The Kirkland Choice lets you change the Bass and Treble too, but it doesn’t have Live Listen.