Got a client who were on 4 iPhone 3GS and had a terrible time with random reboots. O2 gave them 4 free Samsung Galaxy SIII at the beginning of August and they have have just ordered 4 iPhone 5 handsets to replace the Galaxy SIII. The reason? Email calendar and contact syncing with exchange. Sometimes it works sometimes it doesn't plus its spamming the activesync error logs on the server constantly.
They had previously looked at the iPhone 4S but were not sure due to the wonky iPhone 3GS but since then one of the Directors had picked up a new iPad and loves it.
Me, I love that they are doing this, its far easier to manage iOS devices with profiles than it is with ANY android device.