This is an update to a previous version of this tool written by myself and Guy Bachar.
The updated version can now run (and was tested!) on both Lync server 2010 and 2013, and Skype for Business Server.

Run this tool from Lync Management Shell or Skype for Business Management Shell.

Note you will need to run this tool with Local Admin permissions (You will be prompted for elevation automatically if not) and you must have ADDS RSAT installed so you can use the Active Directory PowerShell Module.
You will be asked to provide an Active Directory Group name. Type the Display Name of the group, the tool will reply with the CN of the group, confirming you chose the right group:

Then choose the type of policy (or dial plan) you want to assign this group, there are 14 options:
1     Voice Policy
2     Client Policy
3     External Access Policy
4     Mobility Policy
5     Archiving Policy
6     Hosted Voicemail Policy
7     Client Version Policy
8     Conferencing Policy
9     Voice Routing Policy
10     Location Policy
11     PIN Policy
12     Presence Policy
13     Persistent Chat Policy
14     Dial Plan

After choosing one of the 14 options, you’ll be asked whether you want to assign the global policy to this group or choose from the existing user policies:

If you choose 1 (This is always the Global policy), that will be assigned to the group.
If you choose 2, a new sub-menu will open, detailing the policies you can assign:

You will then be asked to confirm the change and the policy will be assigned the group.

The tool can be downloaded here.