To enable mobile devices to read smartcards we have a range of readers.
With the emergence of smartcards for secure access to, for example, web-sites all devices being used for that conectivity need to be secured. Standard desktop readers cannot normally be attached to these devices because of lack of input ports, so these specialised readers can be used instead so that security is not compromised.
Bluetooth readers also have the advantage of being remote from the device, and can also be used with computers, so that presentation of a card doesn't necessaily have to take place where a computer is difficult to reach.