T-Mobile USA (TMUS +0.2%) has sold 500K iPhone 5 (AAPL +1.1%) units since it began sales on April 12. That's a solid start for the low-end carrier, whose decision to sell the iPhone unsubsidized (with installment plans) could have big industry implications if it goes well. The info was provided in T-Mobile's Q1 report (exc. MetroPCS), which otherwise was ho-hum. 579K customers were added, and branded customers rose for the first time in 15 quarters. But 199K more postpaid subs were lost, service revenue fell 9.9% Y/Y, and adjusted EBITDA fell 7.5% to $1.2B. Branded prepaid ARPU +11% to $28.25, but branded postpaid ARPU -6% to $54.07.