For users of smartphones with data plans:
The best metaphor to describe the cellular networks' billing practices is that of the Unlimited Drink Refill found at virtually every restaurant. You pay for unlimited refills (bytes of data), but the networks charge you additional fees for 'little sips' (160 bytes, the amount used for each TXT). Same premise here, you pay for the bandwidth that's being used to send the message, but you're being charged anyway for the message.
Would you pay for unlimited Internet service at home, and tolerate being charged for every e-mail you send or each website you view?
If your data plan costs $29.99/month for 2GB of bandwidth, each TXT message (160 bytes) should only cost $0.0000024 (or $1 for 416,667 messages).