decide the sender yourself?

Hi everyone, can you please help me correct this:

Send text messages worldwide using all features. You can define the sender yourself.

Many thanks,

TOEFL listening discussions: A conversation between a student and a university advisor[YSaerTTEW443543]

Although both are fine grammatically, I am unsure the second sentence is needed, sensible or appropriate to whatever it intends to say. Whoever opts for these plans is the sender. Why does one need to define oneself in this context? Is that the right verb? Is that the right direct object? Something here seems off.

Hi Mordant,

It basically means that you can insert your own cell phone number or any other number as the sender’s ID. At least that’s how I understand the German original version ;-).[YSaerTTEW443543]

TOEFL listening discussions: Which best describes the student’s current activity?[YSaerTTEW443543]

I would insert “ID.”