I'm using Modem Manager in Debian Jessie and every time when I launch Modem Manager, it requires me to enter admin password:

This is very annoying to enter password on sending/receiving every message. And after quick search I found very simple solution. Below is detailed instruction.

1. In terminal open the following file:
sudo vi /usr/share/polkit-1/actions/org.freedesktop.ModemManager1.policy

2. Find the following 3 entries, we will need their "Action ids" later:

<action id="org.freedesktop.ModemManager1.Device.Control">
<message>System policy prevents unlocking or controlling the mobile broadband device.</message>

<action id="org.freedesktop.ModemManager1.Messaging">
<message>System policy prevents sending or maniuplating this device's text messages.</message>

<action id="org.freedesktop.ModemManager1.Location">
<message>System policy prevents enabling or viewing geographic location information.</message>


3. Create new file:
sudo vi /etc/polkit-1/localauthority/50-local.d/users_modem_manager_policy.pkla

4. enter the following content (replace 'username' with your login):

[Allow user to send messages]
Identity=unix-user:username;
Action=org.freedesktop.ModemManager1.Messaging
ResultInactive=no
ResultActive=yes

[Allow user to control modem]
Identity=unix-user:username;
Action=org.freedesktop.ModemManager1.Device.Control
ResultInactive=no
ResultActive=yes

[Allow user viewing location]
Identity=unix-user:username;
Action=org.freedesktop.ModemManager1.Location
ResultInactive=no
ResultActive=yes

5. Save file "/etc/polkit-1/localauthority/50-local.d/users_modem_manager_policy.pkla"

Now your modem manager will not require admin password.