X0303 4 2011-02-28 1 0001136655 ARBINET Corp ARBX 0001265181 SINGER KAREN 212 VACCARO DRIVE CRESSKILL NJ 07626 0 0 1 0 Common Stock 2011-02-28 4 D 0 1276110 D 0 I As the trustee of the Singer Children's Management Trust The common stock was disposed of pursuant to the merger agreement between Arbinet and Primus in exchange for 742,313 shares of Primus common stock having a market value of $15.60 per share on the effective date of the merger. /s/ David J. Hoyt Attorney-in-fact 2010-03-03