I havent had much experience, had only worked for 2 companies but I have some opnions.
The first company I worked for was a SMB, so as you can figure out, we didnt had a budget for mobile devices. This allowed me and some coworkers to use our personal devices to work with job-related stuff. Truthfully, we were using Google Apps for Bussines at the moment and I, for one, loved the flexibility of having multiple devices linked to that account.
I first had an iPhone when I joined the company, as well as a Blackberry, and I had access to all of my data, i.e: Emails, Calendar, Contacts, Google Docs, etc. What was amazing, was the ability of my employer to wipe my device remotely. Not to mention that when I quit the company they had me bring all the devices to wipe them right there. We wiped the iPhone, an iPad and my Google Nexus.
In the company im working currently at, there is a stronger security compliance regarding mobile devices. The wireless network has blocked access to any device that is not a Blackberry issued by the company or one of the laptops from the company. However, they do grace us with an open wireless network, but this network is even contracted with another ISP, has its own devices and stuff. In no way do the 2 networks interconect, either by HW or SW.
Im not sure if this helps or if other companies work the same way, but this is very much my experience.