It's getting harder to tell your long-distance telephone company's sales pitch from your computer vendor's. Both AT&T and MCI have announced initiatives aimed at business markets in which computing and telecommunications overlap.

In the fall MCI ventured into software with a Windows-based product called NetworkMCI Business, targeted to small to midsize businesses. The much-advertised package includes electronic mail, document sharing, personal-computer-based faxing, and a news-selection service. Dial-up access to the Internet, MCI promised, would be added by year's end. The initial software is pretty cheap at $100, but the ongoing service -- $50 to $65 a month a year -- is not.

Meanwhile, AT&T began tests of its Public Data Services (PDS), which it plans to launch next year. According to spokesperson Marge Boberschmidt, the PDS network will provide some of the Internet's communications advantages, but it will be easier to use and will have improved security. PDS's first service, AT&T Network Notes, will offer Lotus Notes via modem -- so a small company can use Notes without in-house support. However, the Notes service also promises to be pricey, with preliminary estimates ranging from $500 to $1,000 a year per user.