Blaming lower sales volume and a $75,000 write-off from a canceled public offering, ABI American Businessphones said net income declined 13% for its second quarter ended Dec. 31, to $301,000 from $345,000. Revenue totaled $6.6 million, a 7% decrease from the $7.1 million posted a year ago. Net income for the first half of fiscal 1988 rose to $639,000, up 43% from the $447,000 for the first six months of the previous year. ABI said it benefited from a lower tax rate as a result of federal tax changes. Revenues rose to $14 million, a 7% increase from the $13.1 million reported last year. The company said that following October's stock market crash, new system orders from individual business operators declined abruptly and some scheduled installations were postponed, although orders from multibranch, national customers did increase. Fewer installations were completed in the quarter compared to the same period in the prior year; ABI attributed the decline to last year's push for installations before the investment tax credit expired. Irvine-based ABI sells, installs and maintains telephone systems for small and medium-size businesses.