| | re
The reason why you see "webclient" beside using
Using : webclient
is because that's the message service you have selected.
The reason why you don't have any other message services is because you are only on a BWC account.
If for example you were on BWC and BES, then you would have something that looks like
Using : Webclient (if you click u will have the option to change to Desktop)
in Messaging Services -> you will see Webclient and if you click you have the option to change to desktop)
in options/Servicebook you will see Webclient [CMIME] and DESKTOP [CMIME]
otherwise if you check now, you will only notice one service WEBCLIENT [CMIME]
since your question does not pertain to the other servicebook entries, they can be ignored and are fairly self explanatory from the name.
So to answer the question in simple terms, "Using : Webclient" is the messaging service that has been selected through which you send your email.