Students in a MKT3000 class that I taught this morning are doing industry research and one of the questions they need to answer is how many are employed in the industry and is the industry growing? For the wireless telecom industry both the government regulator, the FCC, and the industry trade group, the CTIA, publish surveys that are data rich and include emplyment data. The FCC report is called "Trends in Telephone Service." The CTIA report is the "Semi-Annual Wireless Industry Survey."
Another way to approach this question is to use data from the Bureau of Labor Statistics. You will find industry-specific data in their report on Employment, Hours and Earnings from the Current Employment Statistics Survey. Go to the BLS Data page, find this report, and use the icon to "Create Customized Tables (One Screen)." Then just follow the steps.