I am creating sub admin users from Magento Admin Panel (System->Permissions->Users->Add New User). Here I want to add 1 custom field to save mobile number of each sub admin. I searched it but I didn't got any clue. Please help me to achieve it. Thanks in advance.
For doing so you need to create a new column in admin_user table and rewrite edit user form block to add new element. Element name should be same as new column name that you have created. Then refresh cache and you are good to go.