You don't need a receptionist—or a pricey PBX phone system—to handle your business calls professionally. New cloud-based office phone systems run on mobile devices and automate answering so nobody is left hanging.

Line2 Pro, an app for Android phones, iPhones, and the iPad, can forward incoming calls to up to six other phones (landline, mobile, or other Line2 numbers) simultaneously. You can set up routing by department—so callers can, say, press 2 for Accounting—or automatically route recognized callers to a particular line (say, always sending a key client to the same salesperson). Text messaging is included in the plan, and voice mails are sent as MP3s by e-mail.

The main line costs $15 per month; additional numbers are $10 per month with a 99-user max.

AT&T Office@Hand requires an AT&T phone (BlackBerry, iPhone, or Android) as the main line. If no one picks up, the system can forward calls to up to four other numbers, one at a time or simultaneously. As with Line2, you can configure department routing and automatic routing of specific contacts. The system doesn't support texting; voice mail is sent via e-mail. The iPad app doesn't run full screen.

Cost is $16 per month per user, with a two-line minimum and an 800-user limit.