iPhone 3g dialed number by itself

Today morning my 2 year old was holding my phone and trying to unlock. He tried few pass codes and the phone disabled. After 30 mts, I took the phone to go to work. At 9:10 am I got a call from a 1800 number but no one was there. I hung up the call. Around the same time I noticed there was a outgoing call(at 9:10 AM) to 899-999-99 (yes one digit missing). Also my phone started reducing the volume or or goes to vibration mode by itself. Any idea what could be wrong? My phone is no longer in the warranty.
iPhone 3G iOS 4