No discussion of software upgrades would be complete without some mention of legal-market-specific applications - the solicitors accounts and case-management systems that remain at the core of most law firm IT projects.

Because this is very much a niche vertical market, the typical business model involves a one-off cost for the purchase of the software (technically, you do not 'buy' the software but merely acquire a licence to use it) and related services, including implementation and training, plus an annual maintenance charge of between 10-15% of the cost of the software.

It is also usual for the maintenance to be payable from the point the system goes live, so your total cost in the first year is the capital sum plus the maintenance charge.

So far so good, but the tricky part is ascertaining just what you actually get for your maintenance charge.

For example, a typical charge will cover the use of the telephone helpline, remote diagnostic support via modem and any statutory changes to the software necessitated by legislation or by changes in the mandatory rules of professional governing bodies.

This clearly covers such things as changes in VAT rates and amendments to the Solicitors Accounts Rules.

But would it cover a more fundamental change, such as the introduction of the deposit interest rules a few years ago? Would that class as a change in the rules or the provision of additional functionality and therefore be a chargeable extra?

Then there is the issue of third-party software products either embedded within the system or else required before it will function properly.

The most common instance of this is the database that underpins the modern practice-management system.

Some of these, particularly those designed for smaller firms, are free, whereas others are a chargeable extra - but do watch out for any maintenance charges, as you could find yourself looking at an additional bill you had not budgeted for.

Finally, what about upgrades? Most suppliers operate on the basis that bug fixes, patches and modifications are provided free of charge to all users on a maintenance contract.

But what about more substantial amendments?

Some suppliers now take the view that it is cheaper to have everyone using the same version of software rather than insist they pay for some upgrades and as a consequence have support staff looking after several different versions of the system.

But you must investigate these options thoroughly, not least because few suppliers even present this kind of information in a common format in their quotations.

Charles Christian is an independent adviser to the Law Society's Software Solutions Guide.