Virtual Desktop Infrastructure
Solves many of the problems of BYOD. All you need is two pieces of software - a VDI client and a strong, secure VPN - that can be installed on a wide range of devices (there are plenty of solutions covering RIM and Apple, as well as most Android and Linux systems). WiFi in your offices (with an air-gap to the corporate network) and you're good to go.
I'd be the first to admit that not every application is suitable for VDI - CAD/CAM, software development, some marketing activities are obvious examples. But 90% of users (and in many organisations 99% of users) only need email, Internet/intranet browsing and standard office tools, which are well supported.
Do it right, and you'll find the support costs for your existing desktops will go down as well,.