Here is how IT-Director.com explains the concept.
BYOD or Bring Your Own Device is exactly what is sounds like and, as a policy, is gathering pace. The concept is simple; give a fixed financial allowance to staff and let them buy a device of their choice. This gives employees the choice they inevitably want and removes hassle and cost of providing support services for IT managers (well, some of it anyway). There are obvious policies and procedures that are needed to enable this—not least the provision of Citrix to allow secure access to data from “untrusted” devices and suitable maintenance contracts purchased with devices, but it is certainly a novel way to solving a complex issue. A blue sky concept, possibly, but certainly not pie in the sky because, as cloud computing gathers yet more pace and SaaS is increasingly adopted, this model becomes viable. BYOD has already been rolled out across Kraft foods and the Law Firm SNR Denton.
There are many things that need to be changed to have a concept like that working fine. Most of them in the security area. The other problem that I can see is that in my experience most of the users do not know fully the devices that they own and they use less than 50% of the features on those devices. This will force IT to spent more time in training and if you have a rainbow of devices that will become easily in an IT Management issue.