Fixing these kinds of problems is a process of elimination. There is no single fix for all voicemail problems so trial and error is the theme of the day: try one of the solutions below and then retest. If it works, great. If it doesn’t, move on to the next possible solution.
As a matter of fact, some reports that have explored the decline of voicemail say the service is really only used by two types of people anymore: older parents and business people. But that still doesn’t lessen the annoyance of the receiver when they have to listen to the voicemail from mom and pop or the used car sales guy.

Apple repairs iPhones at the Genius Bar in Apple Stores and through their online mail-in repair service. Apple repairs are high-quality, but out-of-warranty repairs can be much more expensive than third-party solutions. If you're looking to save some money you're not covered by Apple's warranty, you may want to check out our other recommendations.
You don't need an app to record your calls with the 3-way calling described above. There are several paid services that let you call them direct to get the recording going before you pull in the other party. This also means you're not limited to iPhone only—they'll work with an Android phone, or even a landline.