By default, all the users will have Read Only access to the Mobile Edition.
For Read/Write access: In Old Pricing(Users who subscribed for the mobile edition before 15th June 2013) - The administrator needs to purchase the Mobile Add-on and activate it for the users. In New Pricing (Users who subscribed for the mobile edition after 15th June 2013) - Mobile Add-on is available only in the Professional and Enterprise Editions. By default, all the users in Professional and Enterprise Editions will have the Read/Write access. Administrator can disable or enable the access in the Profiles. Go to Setup > Users & Permissions > Profiles > GeneralPermissions > Mobile Edition.
For Trial Version: In Old Pricing(Users who subscribed for the mobile edition before 15th June 2013) - A Maximum of 5 users can use the Trial Versions In New Pricing(Users who subscribed for the mobile edition after 15th June 2013) - Users will be able to try out this feature only if they enable the trial version of the Professional or Enterprise Editon.
For Users in the Old Editions
Purchase Mobile Edition licenses - You can purchase the mobile edition licenses from the Manage Subscription page. The total number of licenses that you buy can be activated for the user and can be used in any or all of the devices mentioned above.
Activate mobile edition licenses for users - For Zoho CRM users to use the application, the licenses that you purchased, need to be activated for them. As long as the user has the license activated, he or she can use the CRM app in iPad, iPhone, Android and BlackBerry devices.
Download and install the app in your device - The users with the mobile edition license activated, can download and install the app in their devices.
Only Users with the Administrator's privileges can subscribe to the Mobile Edition. After subscribing, the Administrator can give access to certain users based on the number of Mobile Edition licenses purchased.