The two fundamental differences between TIM Professional and TIM Plus versions, and TIM Enterprise is in the way that it stores its call data, and its directory information. Here are a few of the other differences:

Distributed directory
TIM Enterprise includes a distributed directory as standard, meaning your employee directory can span multiple sites, with no limit to the actual depth. Aside from the usual user and telephone information, customised fields are available for items such as e-mail address, office location, and so on.
Unlimited hierarchy
With unlimited directory objects (users, extensions, channels, trunks, PBXs) you can faithfully recreate any organisational structure, with as many TDM or IP PBXs as you like.
Unlimited Reporting Collections
Reporting collections allow you to collate separate groups of users from across your entire organisation. No longer are you constrained to your actual organisational structure. For example, TIM Enterprise also allows 'virtual groups' for reporting purposes only so you can report on all of your sales teams from across the world, and compare like-for-like, as a single virtual group. Groups can be served by any number of PBXs from anywhere in your structure.
Use Duplicate Extensions
Multiple PBXs can now use the same or similar extension number ranges, because each PBX is unique in terms of management and reporting.
International timezone reconciliation
When logging multiple sites, whether fed by a single switch or with different PBX's on each site, you will need to have the ability to date and time stamp each calls with the local date and time stamp and not that of the host machine where its logged.
Intelligent Inter-Site Trunk Routing
Simply define the relationship between a group of trunks on one site, and it's counterpart group at another, and TIM Enterprise automatically reconciles CDRs from both, costing them using customised tariffs, or zero-costing them as 'on-net' (or internal) calls.
Mobile CDR Billing
TIM Enterprise users don't just have extension numbers - they have mobile numbers, too. So now carrier-provided mobile CDRs can be processed in the same easy way as standard PBX call logging CDRs - you don't even have to set anything up, it's automatic! SMS and data is supported as just another transaction type and is stored centrally for reporting and integration with 3rd party products.
Multiple Tariffs
If you have several sites, there no guarantee that you use the same tariff provider on all. You may not even be costing in the same currency. TIM Enterprise with any tariff or currency you choose.
Runs as a Windows Service
TIM Enterprise runs as a Windows Service, ensuring high-availability with auto restart on failure, and with inherent unattended execution, your server doesn't require any user intervention - it runs automatically at start-up, without even having to log on.
Unlimited Remote Users
Remote users are given access to a defined point in your organisational tree, where they can administer the system, view statistics and run reports, from anywhere using a standard web browser. There's no practical limit to the number of remote users. As with all Tri-Line products, security is of paramount importance and users access can be restricted to allocated reporting areas only or restricted based on IP address.
Unlimited Live Statistics
Stats collection points can be defined at any point in your directory, and call can affect more than one point, allowing unlimited up-to-the-second display boards for any division, cost centre, group or individual across your entire organisation. We place no limit on the number of Stats Collection Points, Leader boards or Display boards you can use and do not charge for these; they're simply bundled in the price so you help yourself.
Open Standards Interfaces
TIM Enterprise embraces open standards, and provides many interfaces for attaching third-party applications such as call recording, hotel front of house, CRM, screen popping, company diaries and even door entry systems! Using XML, HTTP, and other widely-adopted standards, there are no restrictions placed on integration with the central directory and call databases, when given appropriate permissions.
Uniquely Flexible Pricing
TIM Enterprise is the only enterprise-class call logging system that allows complete flexibility in size and spread of deployment. It prices well on multiple sites with a low port count, or few sites with a high port count, or even a mixture of both!