In one hand is my personal smart phone. I love it. I pay for unlimited voice and data with this phone. I can surf freely and without guilt that I'm wasting government money when I do so. It's also faster and more flexible than...what I hold in my other hand, my blackberry. I hate it. I only use it for government business which is largely viewing e-mails when I'm off site. So I carry two of these devices around. I'd prefer to carry just one. Feel free to keep me electronically leashed. I have no worries over that, but let me have one device. I'll pay the bill. Worried about the security of my e-mails? The cost of an android app that keeps them separate and secure or having me access them through Outlook Web Access is cheaper than paying countless cell phone service bills that aren't really needed.
If you let us opt to use our own cell phones: the government wins due to reduced voice/data/maintenance costs; We win because we don't have to haul around a second, redundant, and obsolete device (Look at what's happening to the market share of blackberry. The public is speaking aobut what they think of these vs. other devices.); The environment wins because there are fewer chargers plugged in in vampire mode waiting to charge yet another smart phone battery.
Also, for responders, such as the U.S. Coast Guard or other law enforcement, this decreases the number of items that you're bringing out in the field with you. The just-one-more-item adds up quickly. Additionally for responders, my cell phone's camera is much better than the one on any blackberry I've had. I've often used it on scene so that I can transmit time-sensitive images/video to the Incident Command Post.