One of the biggest road blocks when it comes to deploying OCS 2007 R2 is the lack of iPhone support.
Sure, you can use Windows Mobile devices, and yes, they rock. I love Windows Mobile. The new WM 6.5 version is even better.
However, I have also learned to love the iPhone and realize that there are way too many decision makers that use the iPhone to ignore it as a platform.
Thanks the team at Modality, there is an option that enables the use of the iPhone as an OCS mobile client. Check out their website at http://www.modalitysystems.com/idialog for more info.