In what is seen as a breakthrough for heavy users of wireless phones, such as businesses, three major phone companies last week introduced new plans doing away with minute usage charges.

Verizon Wireless was quickly followed by AT&T and T-Mobile - three of the four largest wireless phone companies - announcing the new flat-rate plans, which cost about $100 a month. All three companies had their new plans available by the end of last week. Sprint, the fourth of the large phone companies, said it is testing a flat-rate plan.

In its announcement, Verizon Wireless said it was targeting the 13 percent of customers who are the heaviest phone users. Customers will be able to switch to the new plan and back-again without penalties, Verizon said. The basic plan costs $99 per month and covers domestic voice calls and some Internet use. For an additional $20 a month, customers can add text messaging. And for a total of $139 per month, video and mobile e-mail are added.

AT&T’s plans are similar to Verizon’s and includes Apple’s iPhone.