This article considers a Monte-Carlo based methodology for estimating a probability of intermodulation interference in a cellular wireless communication network while accounting for not only the fulfilment of time, frequency and power conditions for its occurrence, but also the effect of random user location in their respective cells and the impact of shadowing. The probability is estimated as the product of three probabilities: probability of the availability of two or more active frequency channels; probability that, the frequencies of the active channels satisfy the intermodulation interference frequency condition and probability that, the active channels signal powers satisfies the intermodulation interference power condition. We present the simulation results for the probability of two and three signals 3-rd order intermodulation interference as a function of cell radius, network traffic and the maximum number of available channels when this methodology is implemented for a GSM 900 standard cellular communication networks.