Best answer by BobTheElectrician
You can close your account and be stuck with paying the tab balance in one shot plus whatever balance of service you owe, and you will lose your number.
If you are looking for a replacement in the immediate future, buy a new SIM now and get your plan switched over to that to avoid any bill padding. Crank your plan down to something smaller, including seasonal hold, until you have the replacement.
You can buy the replacement for cash and continue paying down your old tab, or clear the old tab and get something on a new tab, but only 1 tab at a time. And only one plan change free of charge per billing cycle.