Say the blockchain's growing by a gigabyte a month.[1] I don't think SMS can support that much, especially times so many devices. Using a tv signal is more robust - you can support millions of devices, and transient 3G network failures will have less or no effect.

[1] I estimated. http://blockchain.info/charts/blocks-size

But the parking meter (etc.) doesn't need to handle the blockchain at all. It could use the SMS to communicate with a shared parking meter bitcoin transaction server. That said, broadcasting the blockchain is useful.

If you stick to centralized solution then that would work nice and might be good enough. However Kryptoradio allows to do it by just listening incoming transactions and blocks.

The idea is that a lot of devices wouldn't need a two-way connection, rather they could confirm payment with only a downlink.