Should I be wary of these strange phone calls I've been receiving?

For the past six nights, I've received strange phone calls from an unrecognized number around 3 AM on the dot. I usually don't answer late night calls, especially from numbers I don't recognize, but the number was abnormally strange, so I did. When I answered and said "Hello?" the first time, there was no verbal response and the only thing I could hear was creepy, deep breathing. Every night it's been the same- I answer and all I hear is the breathing. The number is 090-4444-4444 and I believe the calls are coming from a different country. When I try to call back, the number is always disconnected. What would you make of this? Strange, right? I'm waiting to see if it happens again tonight.