My measurements show that the Skype Android application is using 14.89 KB of data per hour when on standby. This data is used for maintaining the connection to the Skype servers and checking for instant messages. Over a month this would add up to about 446 KB (less than half a Megabyte).
According to the Skype web site:
- Voice calls to other Skype users use 50kbps or around 3MB for one minute of calling.
- Voice calls to to mobile numbers or landlines use 6-20 kbps or around 1MB for one minute of calling because the audio quality is lower than for Skype to Skype calls.
- Video calls between two mobile phone devices: 500kbps (30MB per minute)
- Video calls between a mobile phone and a computer: 600kbps (36MB per minute)
Instant messaging would presumably not use much bandwidth.
There is also a warning on the Skype web site:
Having a large number of contacts on your Skype account also increases the data usage, as the application has to update more contact information, such as statuses, profiles and mood messages.So if you made a five minute voice call to a Skype user every day for thirty days the total usage over that period, including standby would use about 451 MB of bandwidth.
This is my calculation - but I could be wrong. Use this prediction with caution.