We describe an Internet application for providing mobile phone tariff information for Northern Ireland and the Republic of Ireland. Using this application it is possible to accurately and easily determine and compare mobile phone packages offered by different service providers. One of the important features of such an Internet application is the potential for high maintenance associated with the data in the system and more importantly the structure of the system given the inevitable changes in the corresponding mobile phone market. We have identified the maintenance tasks associated with our system to reflect changes in the mobile phone market and outline an evaluation technique for describing the system's ability to cope with change. In particular, we evaluate the actual change required to our software system to implement various maintenance tasks. We have found that there is an upper bound (˜5%) on the maintenance effort associated with the system which is both acceptable and manageable for maintenance purposes. We show that at most the changes required to our system are no greater than 3.07%, when a complete new service provider is added or removed. We conclude that the development of a maintenance model in conjunction with system design is essential for estimating the maintenance effort associated with similar Internet applications.