This thesis takes a deeper look into customer behaviours when it comes to buying new mobile phones. We take a look at four main types of planned obsolescence we’ve found, which include: economic obsolescence, obsolescence of function, obsolescence of desirability and obsolescence of quality. With a questionnaire and focus group study we try to find out the underlying reasons why users buy new phones while their old ones are still functional. Since this is not a new subject, we try to map the problems we encounter in our study to the four already defined forms described above, and we try to see if there are other forms that are not yet defined. What we found out was that these four categories hold up very well, but are not as separate as one would have thought when reading. While we find out many reasons why people change their phones we do not offer a solution. But we do offer a better understanding of the problem and hope the consumer will take part of the knowledge.