B26354, I know the importance of understanding the calls on your billing statement. This can help you better manage your account and options. I can explain why these calls may display on your bill without a phone number. Sometimes depending on the other carrier or where your located, the number may not be captured by our system. Calls that show up with a number of 999-999-9999 can be unavailable calls, blocked, or restricted calls. Also, calls that are received in Extended network areas may also display unavailable or 999-999-9999. Additionally, when a person dials *82 on their phone before placing a call, the phone number will be blocked and will show up as unavailable, restricted, or 999-999-9999 on your bill.
I hope the above explanation helps with understanding your calling details.