Global shipments of handheld computers fell for the fifth consecutive quarter, squeezed by surging demand for devices that combine cellular telephones with palmtop organizers, market research firm IDC said on Wednesday. Shipments of 1.9 million digital organizers in the first quarter were down 12 percent from the same period last year and 31 percent from the fourth quarter, IDC said. By contrast, the worldwide converged mobile device market kept up its torrid growth, with shipments rising 135 percent year-over-year, its third straight quarter of triple digit growth, to 8.4 million units.