OUAnthony is correct. Here's some more details on the bandwidth usage:
When an iCamSource is idle it is sending a small amount of data (about 100 bytes per cameras) every 5 seconds or so to the iCam Broker Server to let it know it is still there. That equates to about 61 MB of data uploaded per month for each camera from your computer if it is just sitting there 24 hours a day, 7 days a week. When an iPhone is connected, then naturally the image data being uploaded to the phone will be added to the total. Push notifications can also add to slightly to the total bandwidth.