When no one is actively connected to or streaming from the Slingbox, the amount of bandwidth used is minimal. The Slingbox will send occasional updates to Sling Media's servers when its IP address changes, but the amount of data sent is less than 100KB.
The Slingbox uses more data if a firmware update needs to be downloaded (less than 100MB), but even that only occurs once every 2-3 months for current Slingboxes. There have been no updates for the SOLO in well over a year.
Hope this helps!!!
Sling Media Moderation Team