Believe it or not, there's a stealth bull market going on even in the red hot wireless industry, James Cramer said Wednesday on "RealMoney" radio show . Cramer said he has spent weeks telling listeners to play the wireless boom by buying handset giant Motorola ( MOT). But Cramer said Wednesday that he's got another way into this scorching sector: buying the shares of the companies that own cell-phone towers. After all, Cramer notes, big players like Verizon Wireless and Cingular and Sprint ( FON) are adding users at a rapid clip, and to keep pace with demand they're going to have to improve service. But building new cell-phone towers is expensive, so how to upgrade? By putting more antennas on existing cell-phone towers. That should drive up shares in the big cell-phone tower players, Cramer said. He said he is most impressed by Global Signal ( GSL), calling it the best-of-breed pick. He said he likes the insider buying at the company, as well as its "fat" 4.2% dividend yield. Cramer said rivals Crown Castle ( CCI), American Tower ( AMT) and SpectraSite ( SSI) are less compelling, with Crown Castle tarred by the insider-selling brush and American Tower and SpectraSite moving toward a big merger. Cramer said he won't tell listeners to play mergers because of the risk. "The more time I spend looking into infrastructure, the more I think there's money to be made," Cramer said. He said these stocks are way up this summer but remain cheap for the most part. Cramer said he doesn't own any of the tower stocks right now, not that he's happy about having missed a 19-point run-up in Global Signal.