It all depends what services you offer at your GSM store. Many stores have applications related to unlock and diagnosing, since most of the jobs will have to be performed on the phone with the required tools. The software part requires hardware boxes that you need in order to access phone's protected areas (system partition, EFS partition, etc). My advice is to visit a local GSM shop and they should tell you the tools and software used in the process of phone servicing.
