* Says found errors in billing process related to Sprint
* Shares down 22 pct
April 20 (Reuters) - Ntelos Holdings Corp NTLS.O cut its 2009 revenue outlook to reflect billing errors related to its largest customer Sprint Nextel Corp (S.N), sending its shares down 22 percent to a two-year low.
The company's wireless operations comprise a Ntelos branded retail business and a wholesale business that it operates under an exclusive contract with Sprint.
Some of the usage by Sprint customers was incorrectly classified in Ntelos' billing process, Ntelos said in a statement. Sprint, the No. 3 U.S. mobile company, accounted for about 22 percent of Ntelos' 2008 operating revenue.
Ntelos' 2008 wireless wholesale revenue was overstated by about $3.9 million, or 0.7 percent of previously reported consolidated revenue, due to the billing error.
For 2009, the company sees revenue of $562 million to $571 million, down from prior expectations of $574 million to $583 million. [ID:nWNAB4962]
Shares of the company touched a low of $13.90 before recouping some losses to trade down $2.39 at $15.53 Monday on Nasdaq. (Reporting by Shrutika Verma in Bangalore; Editing by Anne Pallivathuckal)