To replace the card, you will need to visit a Sprint Store or participating retail location. The card itself has no value so no one else can use your card to add funds to a different account. Someone can add funds to your account if they wanted to, but that is not likely. Yes, it is possible to have multiple cards on a single account. Optional services such as Roadside Rescue, Equipment Replacement, and Sprint PCS Voice Command are not automatically subtracted from your Monthly Spending Allowance.
Separate payment is required for all optional services.
We recommend that you pay for your optional services at the beginning of your billing cycle. Due to data delays, the balance available for use is only an estimate and may vary from your actual available balance. Another possibility is that you have optional services on your plan and you haven't made any additional payments. Optional service fees do not come out of your Monthly Spending Allowance and they do not count against your Minimum Spending Amount. You will need to make an additional payment each month to continue using your phone without interruption of service.