Softbank Corp. said Thursday that it had its best month in four months in July after starting to sell Apple Inc.'s iPhone 3G.

Softbank had a net addition of 215,400 subscribers last month for a total of 19.3 million, the company said. The increase is its biggest since March, when it gained a record 543,900 users after introducing free calls between family members.

Discounts and installment payment plans helped Japan's third-largest mobile phone company add more users than NTT DoCoMo Inc. and KDDI Corp. for 15 straight months. Softbank is counting on the touch-screen iPhone 3G, which combines an e-mail-equipped handset with the iPod media player, to maintain its lead in customer gains and bolster earnings from data services.

DoCoMo, the biggest mobile-phone operator, added a net 94,200 users for a total of 53.7 million in July, and KDDI, the second-biggest, gained 17,000 to 30.3 million. The companies reported the figures separately Thursday.

Softbank is offering the 8-gigabyte iPhone model for ¥23,040 and the 16-gigabyte version for ¥34,560 for new users, with existing customers paying more. Subscribers have the option of paying for the handset over two years.