In an amusing mob rush, and as a follow-up to yesterday's announcement, Reuters reports that AT&T, Verizon Wireless and T-Mobile USA on Tuesday all announced flat rate plans for unlimited calls in the United States. It wasn't just them, either—Helio and Sprint both did the same thing recently. But Sprint's plan was more expensive (even though it includes data, unlike yesterday's announcements) and Helio is just too small to raise much notice.

At any rate, the article said that the unlimited plans are raising investor concerns that a price war could break out and send shares lower.

Verizon and AT&T's plans both cost $99 for unlimited calls, although data and messaging are extra. T-Mobile's $99 unlimited plan includes messaging as well.