T-Mobile USA earned the highest score among the four major nationwide carriers in the latest Consumer Reports ranking of cellular service providers. But the gaps between T-Mobile, Verizon Wireless, AT&T, and Sprint weren't very large, as the big four all lagged far behind the smallest carriers in customer satisfaction.

Consumer Cellular came in first place out of 10 postpaid carriers with an overall score of 89 out of 100, followed by Ting, which scored 88. The next four carriers were GreatCall/Jitterbug, Credo Mobile, Virgin Mobile, and US Cellular, which all scored in the 70s.

The big four occupied the bottom four slots. T-Mobile scored 73, followed by Verizon at 70, AT&T at 68, and Sprint at 67.

Consumer Cellular resells AT&T and T-Mobile capacity and recently passed 2 million customers, a far cry from the 137.6 million and 126.4 million claimed by Verizon and AT&T, respectively.

The big four also pulled up the rear in Consumer Reports' pre-paid rankings with similar scores and in the same order. Among 13 prepaid services, Republic Wireless and Cricket led the way with overall scores of 87 and 85, respectively. Next in the ranking were Page Plus Cellular, Straight Talk, TracFone, MetroPCS, Virgin Mobile, Net10, Boost Mobile, T-Mobile, Verizon, AT&T, and Sprint.

Consumer Reports described the results in an article, but the group asked us not to republish the full ranking table, which is available to subscribers. Based on a survey of 90,000 subscribers, the carriers were rated on value, voice calls, texting, Web problems, data, phone support, support staff knowledge, and support staff courtesy.

In total, 80 percent of survey respondents were customers of the big four, and 81 percent of those were AT&T or Verizon customers. Consumer Reports argues that customers aren't switching phone providers often enough.

"Nearly half of the people who switched cell phone carriers in the past year saw their monthly rates drop by $20 or more," the group wrote. "And roughly 40 percent said they enjoyed more reliable coverage, faster data service, and better customer service. However, only 6 percent of our readers switched cell phone carriers—perhaps more should consider shopping around."

The main reason customers switch carriers is to get better coverage, which benefits AT&T and Verizon, the group said. "They have the country quite well-covered with high-speed 4G Internet service. There’s no point in finding a great deal if it doesn’t let you receive phone calls in your home or office," Consumer Reports said.

But the deals from small carriers are worth checking out if you can get good coverage. The smaller carriers are best suited to people "with modest data needs (Web browsing, e-mail, Facebook) and little lust for the hot phone of the moment," Consumer Reports said.

The smaller carriers are often mobile virtual network operators (MVNOs) who purchase capacity from larger carriers and sell to consumers at lower prices. In some cases they're subsidiaries of the big four. AT&T owns Cricket and T-Mobile owns MetroPCS, for example.

These smaller carriers beat the big ones with "lower costs and responsive, knowledgeable staff members" and innovative offerings. "Some of them compensate subscribers who use less service than they've planned for," Consumer Reports wrote. "For instance, Republic Wireless and Ting Wireless charge customers only for the minutes, texts, and data actually used—not what consumers signed up for."