In Canada, if you have Rogers wireless as your cellphone provider, they offer a My5 and My10 plan, where you list the 5 or 10 people you talk to the most, and their numbers are excluded from fees like daytime minutes. The issue is, you can only set this once a month, and often forget about it. It would be great if there was an android app that detected monthly who you spoke to longest during the workdays (evenings and week-ends are often included) and automatically changed your MY5 or My10 accordingly, once a month. I've found apps that show who you call the most often, but this is not necessarily the same person you talk to the longest during the workday (used the most minutes with).
If you know of such an app, please let me know!