T-Mobile and Cingular have suspended sales of Motorola's Razr cell phones because of a bug that causes some of the ultra-thin mobile phones to drop calls.The problem affects "a very limited number of Razr handsets sold for GSM [Global System for Mobile Communications] networks over the last four weeks," said Alan Buddendeck, a Motorola spokesman. Only T-Mobile and Cingular have suspended sales of the phones, he added."A handset that has this issue may disconnect calls, power down and then automatically restart," he said. Motorola is not saying what component of the Razr is responsible for the problem or what specific Razr models are affected.Motorola and the wireless carriers have taken steps to ensure that customers can exchange defective phones, according to Buddendeck.The two carriers suspended sales of the phones earlier this week so that Motorola could go through inventory supplies and recall systems with the affected component, a process that should soon be completed, according to Buddendeck. "Within the next week, we expected everything to be back to normal with respect to availability," he said.T-Mobile began pulling Razr V3 phones from retail outlets on Wednesday, said T-Mobile spokesman Peter Dobrow. "There was a defective component in a limited number of shipments to us from Motorola during the month of February," he said. "Since there's no way to tell at retail which units [were defective], for the best interests of our customers we pulled them from our shelves."T-Mobile customers with defective Razrs should call the company's customer support line to arrange for a replacement phone, Dobrow said.Motorola does not expect the recall to have "any impact on financial results," Buddendeck said.Representatives from Cingular were not immediately available to comment for this story.T-Mobile's customer support number in the U.S. is 1-800-937-8997.