You can import your own addressbook by clicking Add from file... link. The file can have Excel, csv, vcf or txt format.
You can easily save recipients to a new list by choosing Save recipients from To-menu. You can create as many lists as you want.
You can paste recipients’ numbers from clipboard to TO-field. Numbers will be automatically collected from pasted text.
If you frequently send the same messages to customers, save the message as a template under the Message menu.