Verizon Wireless kept up the beat with strong second-quarter subscriber growth. This nation's No. 2 mobile phone service says it added 1.8 million net new users in the quarter ended in June. The big gains take Verizon Wireless', a joint venture between Verizon ( VZ) and Vodafone ( VOD), total subscriber number to 54.8 million. Verizon Wireless has been steadily gaining market share in the cell-phone service race. Cingular -- co-owned by AT&T ( T) and BellSouth ( BLS) -- with 57.3 million customers, has seen its net subscriber growth cool down over the past three quarters. And industry observers are concerned that No. 3 wireless player Sprint ( S) may have lackluster numbers when the company reports Aug. 3. Verizon Wireless did not provide a monthly customer termination, or churn, rate, nor did the Basking Ridge, N.J., tech shop disclose the all-important average revenue per user number. The company is scheduled to report earnings on Aug. 1. Analysts had been looking for Verizon Wireless to post net subscriber gains of 1.6 million. Industry watchers and analysts attribute Verizon Wireless' strength to its popular family plans and effective "reliability" ad campaign. Verizon shares rose a quarter to $32.12, and Vodafone was up 53 cents to $21.15 in early trading Monday.