When we send or receive bulk SMS on our mobile phone, we always get Sender ID which begins with 2 Alpha characters prefixed to each and every bulk SMS message. What is this and why do we get that? Well, TRAI has categorized in such a way to identify sent bulk SMS message and the sender details. By this, operator would easily understand to trace or identify the bulk SMS user.Let us understand in detail on this and grab the codes too, eh. For example, we receive SMS from our bank, let us take ICICI, when we receive then the sender id would be like this TD-ICICIB. So, here we are discussing on the first two characters of the sender id, that is TD. T as in Tata Teleservices, hence this is a Telecom Operator Code and D as in Delhi, hence this is Regional Code.