Recently committed changes include proper socket closing so sockets will be eventually released.
Seem that Concox GT06N tracking device is very efficient in terms of traffic. Own server implementation allowed me to estimate total monthly data traffic. It is around 1Mbyte/month. This is good. My Swedish mobile/cellphone plan is minimal and nominally costing me 0SEK/month if phone is not used at all. With low data traffic and some configuration SMS (text messages) sent time-to-time the bill will be below 20SEK (~$3.00) per month.