I'd like to use a M2M SIM card in one electronic device. Of course, I would use data (IP) connection over GPRS or UMTS link. There are many offers on the market depending on the mobile operator, but they usually give you a maximum payload versus the payment of a fixed amount of money per month (6?/month for 1GB and similar).
What I can't understand, and sales man aren't able to explain, is how this data traffic is calculated. I have mainly two questions.
Is a single payload byte in a single UDP/IP packet charged as a single byte? If this is true, I could send 1*1024*1024*1024 packets in a month, that is one very 2.5ms. Moreover, if this is true, I can ping a remote device without charging (ping is based on ICMP over IP packets). Or the operator will charge for IP and TCP/UDP packets too (IP header, TCP/UDP header, checksum, ...)?
Another question is: is there a smallest amount of data that is charged even if the data really transfered are less? For example, when I open a data connection, the operator could charge me immediately for 1kB. If I send only 10 or 100 bytes, I always pay for at least 1kB. And if I send 1030 bytes, the operator charges for two blocks (that is 2kB).