There have been varying levels of progress towards this.
Bit-Pay offers mobile checkout:
- https://bit-pay.com/aboutMobile.html
- https://bitcointalksearch.org/topic/m.735667
Jav, author of InstaWallet.org created this:
- https://bitcointalksearch.org/topic/ann-release-of-open-source-point-of-sale-system-w-video-38893
MagicalTux of Mt. Gox had been working on something, supposedly, but there has been no date / specifications released.
Weex of ExchB had reportedly been working on something before closing the exchange and (assumingly) abandoning the P.O.S. project as well.
Casascius had looked into using Veriphone swipers reprogrammed for bitcoin:
- http://en.bitcoin.it/wiki/Casascius_Bitcoin_POS_system
There had been rumors that a P.O.S. software vendor was considering adding a Bitcoin payment option, but that was some time ago and there have been no recent buzz, as far as I'm aware of.
Without any assistance, a merchant can accept bitcoins using Bitcoin Spinner on a mobile for instance.
Thanks