I think for the money the P1 edition is a steal at ?4 or 6$ per seat and you can have upto 50 seats before you need to consider enterprise.
WP does a damn good job setting up the Sharepoint and Office 365 email on your phone and I get the faintest hint that it should also do the same for Lync (Install the App first before adding the 365 Email account).
Lync is a pretty damn fine product especially for presentations and keeping touch with your back office team assuming you have one, both in the office and on the road. Sharepoint also offers a secure area to store you documents and control them.
Lync works reasonably well on the phone but I get the feeling it is just the start. The interesting thing about Microsoft is they are not trying to provide services that only work on a windows enviroment. They have tried that, they now work to ensure that the functionality is available across the broadest spectrum so Macs and Firefox etc are all included in the Microsoft party and most functionality if supported is offered.
Best of all pretty much all of this is available so long as you have an internet browser and access to the internet anywhere you happen to find yourself.