The message length allowed for 1 credit message is 160 characters. If the text length exceeds 160 characters then the message consumes 2 or more credits. The character length for 2 messages is 306, for 3 messages is 459, for 4 messages is 612, and for 5 messages is 724.
You can select your company name or brand name (6 characters) like TD-TSTSMS as your sender id in case of transactional messages. In case of promotional messages you cannot choose your id and messages deliver with the id similar to LM-TESTID.