Oooo that ones hard. ummm... idk i think we should just leave it to the experts ya know.
Let's see: frequency of cellular phone waves (GSM phones) is (800-1900 MHz). If we look at the table of the electromagnetic spectrum, we can see that this range is contained within the frequencies of the microwaves, which include waves in the range 300 MHz-300 GHz.
So, summarizing, the correct answer is "microwaves".
