The momentum is building at Verizon Wireless.

The nation's leading wireless service provider added 1.54 million new subscribers in the second quarter. The net adds number, which was even higher than some analysts had expected, shows that the company is more than keeping pace with rivals in the fast-growing cell-phone market.

The news was noted in a second-quarter earnings release from Britain's Vodafone ( VOD), which is a partner in the wireless venture with New York telco Verizon ( VZ). The report comes as Verizon prepares to release its latest earnings report Tuesday. Analysts expect the gangbuster growth of the wireless unit to largely overshadow the declines of its core local phone business.

Verizon shares rose 78 cents Monday to $36.10, while Vodafone slipped 27 cents to $21.02.

Monday's numbers offer the latest evidence that Verizon Wireless has been growing at a rapid clip. The June-quarter numbers surpass the 1.4 million new subscribers the venture added in the first quarter ended in March. Verizon Wireless now has 40.4 million subscribers.

Vodafone, which has a 45% stake in the venture, said Monday that its portion of net new subscribers was 682,000. That means that 1.536 million users signed on for service in the second quarter ended in June.

When Verizon reports full second-quarter numbers early Tuesday, investors will be focused on whether the company has been able to sustain its solid average revenue per user, or ARPU, levels. Verizon Wireless will also be aiming to keep subscriber defections, or churn, at an impressively low rate.

Some analysts are expecting monthly ARPU to be in the $49 range and churn to fall to 1.6% and possibly lower as the company capitalizes on defections from AT&T Wireless ( AWE) and Cingular, which posted sluggish subscriber gains last week.

Earlier this year, Cingular offered to pay $15 per share for AT&T Wireless in a $41 billion merger the companies expect to close by year-end.

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