The stock exchange ratio is expected to be at market, the sources said. The companies are hoping to reach an agreement by the third week of October.
T-Mobile is owned by Deutsche Telekom while Sprint is controlled by SoftBank, which had also explored a possible combination of Sprint with Charter Communications. That latter transaction was put on hold given the T-Mobile-Sprint talks.
Minority owners would own about mid-30 percent of combined company, sources said.
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