So with the order of the $20 deal for 3 mo w/5gb LTE, Mint included a trial kit with 2 SIMs. Looks like a good way to get a week's worth of cell service. The first SIM allows you to activate and use in your usual places to ensure coverage, the 2nd SIM meant for you to port in your number. Very nice!
The intent of the trial kit is to use the first for the trial, and the second to activate permanent service after the trial. The second SIM definitely won't be a necessity with the 3-month plan (separate SIM shipped for the 3-month promo plan). I've read that both can be used to set up a trial, though. Maybe the second could be passed along to a friend for a trial.