Why is my T-Mobile phone using iWireless tower not working?

Cell phone (T-mobile using iWireless tower) not calling 5 contacts (Verizon all on same family plan).  Busy signal only.  Worked fine until last September on Samsung 3G phone.  Switched to iPhone.  Worked fine for a few weeks.  Not working now. why?

Hi Mary. May have something to do on T-Mobile's end. Please contact T-Mobile and report the problem.

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