A more detailed explanation of issue is below:

Symptoms:

A non-YouMail caller calls you and hears "Please enter your 10 digit number" instead of your voicemail greeting

A YouMail caller calls you and gets logged into their own YouMail account, as if they called us to check YouMail

Why this happens:

Callers can get this error while connected to any of our General Access Numbers because the carrier doesn't properly forward the proper caller-id information (ie. even if the caller-id shows successfully on your phone, it's still possible the caller-id's aren't sent and YouMail doesn't know which account to log the call into.)  With General Access Numbers, thousands of other users are connected to the same one; which helps keep our basic visual voicemail service free by keeping our operations and maintenance costs low.  

If your caller is also a YouMail user, they'll experience being logged into their own voicemail inbox.

Fix:

If you're a Free user, try to troubleshoot the issue. If it does not work,  then you'll need to contact your carrier. However, aside from Sprint, we haven't had any success in getting other carriers to fix the issue on their end. Consider getting a Personal Access Number.

If you're a Premium user or a free user never wanting to experience this issue again, get your own Personal Access Number.