Virgin Mobile USA Inc., a joint venture of billionaire Richard Branson's Virgin Group Ltd. and Sprint Nextel Corp., raised its planned initial public offering to $506 million, five times more than the original target.

The mobile-phone company said in May it planned to raise $100 million in the IPO. Warren, New Jersey-based Virgin Mobile USA didn't disclose how many shares it plans to sell and the offer price in its regulatory filing today. Spokeswoman Jayne Wallace declined to comment.