Pay-as-you-go phone plans sound pretty nice. You only pay for how many minutes you call, how many text messages you send, and how much data you use. The text message fees (usually $0.20/message) are a bit high, but not too unreasonable. Until you do the math:
Text messages are limited to 160 characters. The average text message is probably around 80-90 characters. SMS messages use 7-bit characters. Therefore, the average text message is around 595 bits, or 74 bytes. You are paying $0.20/74 bytes, or $0.003/byte. We can then multiply that by 1,073,741,824 (how many bytes in a gigabyte) to get $2,902,004 / 1 gigabyte.