Exchange 2010 with Device Client Access Licenses - do I need licenses for each smart phone too?

you would want a user CAL instead of a device CAL
that way it covers the user whether using a notebook, tables, phone, etc. as opposed to a device CAL which is per device

As Seth stated you would probably want to look at user CALS in this case.  That being said, you can also mix and match device and user CALs.  Not recommended by Microsoft due to the complexity of keeping up with licensing, however you can do it.  Why would you do this?

A good example is a company that has 450 users and 100 desktop computers.  Of those 450 users, 20 are supervisory users that need access to multiple devices.  They have 20 desktops, 20 laptops, 20 mobile devices and in some cases iPads or other tablets.  To properly license on a device CAL you would need 100 (desktop) + up to 60 (for the additional mobile, phone and tablet).  That would be 160 licenses.

Now consider what can be done:

License 80 devices (covers the desktops) and 20 users (covers the 20 users with multiple devices).  Now you are back down to 100 licenses in totality to cover 450 users across 160 devices.  This would use a mix and match of the users and device CALS.

Also every mailbox does not require a license under user CALS, only every USER.  So a single user could have 5 mailboxes and as long as that user is the only one that access those 5 mailboxes, you only need a single user CAL.

Hope this helps and let us know if you need some more information or if something is not clear.

Thanks for the information - very helpful.
Clearly, we should have purchased user cals right off the bat.  In our case, does not seem like we have any benefit from the device option.
Looks like we'll have to add on the user licenses - but .... does Microsoft have any way to allow a switch to go to the alternate licensing option?