First when the mobile phone became a device for more that voice and sms we started to worry about the different operation systems. Ringing tones and games were down loaded and we started to surf the operator WAP portals. The non voice services were taking off and the enthusiasm was high. This was though shown to be rather difficult to manage for the content providers and operators due to different operating systems and even variations depending on phone model and brand. Many versions of each individual game had to be developed and we had to keep track of exactly what phone model the end user had and sometimes even the software version of the particular phone model.
Read more at the Universal Mobile Interface blog