Despite an analysts' upgrade, shares of Virgin Mobile USA Inc. fell Friday to their lowest point since the company's recent trading debut after the company said its third-quarter loss widened as operating expenses rose.

The wireless service provider's shares fell $1.54, or 14.4 percent, to $9.19 Friday. Earlier, the shares traded as low as $8.07.

Virgin Mobile said late Thursday that its third-quarter loss widened to $7.3 million, compared with a loss of $5.1 million in the year-ago quarter.

The company said its pro-forma loss totaled 15 cents per share, compared with a loss of 10 cents per share in the year-ago period.

Revenue rose year over year to $319.5 million from $271 million, as an increase in service revenue overshadowed a decline in equipment sales.

In a note to clients Friday, Stanford Group Company analyst Michael Gary Nelson upgraded the stock to "Hold" from "Sell," saying challenges the company faces -- such as increasing competition -- are well balanced with opportunities for raising shareholder value.

The analyst called Virgin Mobile's third-quarter results "mixed" and its fourth-quarter outlook for between 350,000 and 400,000 net customer additions "weak." But he also said its guidance for 2008 EBITDA -- or earnings before interest, taxes, depreciation and amortization -- of between $155 million and $175 million is strong.