I work for a company that allows their employees to bring in their own phones, issue is no support and no security. IT is rarely thought of and there is no training on mobile phones for IT to train up on and if they do find training, then you must pay them correctly. Then the employees, are "normally" , lack the knowledge of the phone and opens alot of security holes.
Biggest issues we have are, the phones locking the employee out of all systems, new OSs do not support VPN, and employees not knowing how to use their phones properly with Business Emails and Files. Mainly failure to follow proper security protocols and standards.
My opinion - Switch to Windows Phone 7. Its already intergrated into Windows 7 and 8. Its controlled by Microsoft, since most government systems are Microsoft based, you already have the correct IT infrastructure and upgradeing wont be to costly. And with WP7, any apps made for it will work across the board, with Apple and Android, they may need a new phone to properly upgrade the OS to support the APP. All WP7 phones can support future updates, no need to buy a new phone. The main thing is the strong relationship already built with Microsoft.