It means that most prepaid carriers wont let you forward voicemail to another number, but all you have to do is call the carrier and have them turn voicemail services off for your phone. Then, when it rings, since no carrier voice mail picks up, so if you don't answer the call, it goes to your Google Voice voicemail. Everything works perfectly. The only problem you could encounter with this setup is if you ever gave out the real phone number to your phone (the one your carrier assigns you), there would be no voicemail services for them to use if you failed to answer. However, giving someone your phone actual phone number defeats the whole purpose of you using GV.