UPDATE 1-IBasis sues to halt KPN tender offer

NEW YORK Aug 18 (Reuters) - Wholesale telephone call carrier iBasis Inc IBAS.O filed a U.S. federal lawsuit on Tuesday against Dutch-based Koninklijke KPN NV (KPN.AS), seeking to halt a buyout offer that it believes "grossly" undervalues the company.

KPN, the telecommunications company and iBasis' majority shareholder, last month offered to purchase the 44 percent of Burlington, Massachusetts-based iBasis it did not already own for $48.2 million, or $1.55 per share. Shares of iBasis closed down 1 cent at $2.17 on the Nasdaq on Tuesday.

In a lawsuit filed with the U.S. District Court for the Southern District of New York, iBasis accused KPN of "a blatant effort to mislead iBasis shareholders into tendering their shares for the grossly unfair price" of $1.55 each.

It accused KPN of concealing internal projections suggesting that iBasis might perform better than projected, perhaps justifying a higher share price.

The company also accused KPN of engaging in a "concerted scheme" to drive down iBasis' stock price, so that it could buy the rest of the company at a "dramatically reduced price.

KPN did not return a request for comment.

Last week, it said it asked the Delaware Chancery Court to invalidate an anti-takeover measure known as a "poison pill" that iBasis, which is based in that state, sought to invoke.

In Tuesday's lawsuit, iBasis is seeking to block KPN from buying its stock absent further disclosures, to halt further misstatements and omissions, and other remedies.

The case is iBasis Inc v. Koninklijke KPN NV et al, U.S. District Court, Southern District of New York (Manhattan), No. 09-7288. (Reporting by Jonathan Stempel; Additional reporting by Alexandria Sage in San Francisco)