You receive a letter or an email telling you there are government job openings in your area, and a number to call for more information is provided. You call the number and wait on hold--it is the government, after all. Ten minutes later, you realize you have to be somewhere else soon so you hang up the phone.
You try again the next day and are faced with the same long wait. After a few more calls, you give up and stop calling. You don't want to be a part of that bureaucratic monster anyway. A few weeks later, you get your phone bill and your jaw nearly hits the floor. You see hundreds of dollars in "premium" calls over the last few weeks.
How to avoid: the government generally doesn't send out letters or emails about job openings. Scammers do. If you do get such an email or letter, check the government job board online. And above all, don't call unless it's a 1-800 number.