No harm in asking support. If you're looking at less than 10 mins/mo, that seems consistent with the intent of the softphone option. If you do submit a ticket, please update this thread with the response.

Sounds like you don't work for a large company. I was being a bit facetious about the electricity, but bandwidth consumption and (more importantly) network security/unauthorized devices can get one into hot water with employers. For example, many companies prohibit audio streaming (internet radio) by employees. While 10 mins of phone conversation per month would amount to far less bandwidth than 8 hours of streaming, some companies' network policies are not so forgiving.