I've considered a cheap backup phone just in case I ever have to have a repair on my phone that will either require leaving it at an Apple Store or Best Buy longer than I can wait in store or will require sending it away.
There are unlocked 4G phones such as the Nokia 225 for under $50 and the Nokia 6300 for under $70.
I could then either use the SIM from my iPhone, or if I didn't mind using a temporary number instead of my regular number while the iPhone is being repaired Mint Mobile has a "try before you buy" kit for $2 that includes a SIM and new number that is good for one week of service. It is meant to let people test out Mint Mobile before switching to make sure coverage and service are satisfactory, but seems like it would also work for someone who just wanted temporary service.
There are unlocked 4G phones such as the Nokia 225 for under $50 and the Nokia 6300 for under $70.
I could then either use the SIM from my iPhone, or if I didn't mind using a temporary number instead of my regular number while the iPhone is being repaired Mint Mobile has a "try before you buy" kit for $2 that includes a SIM and new number that is good for one week of service. It is meant to let people test out Mint Mobile before switching to make sure coverage and service are satisfactory, but seems like it would also work for someone who just wanted temporary service.