My phone receives texts but cannot send them...

[Android Central Question]

I have a Galaxy S5 phone and I have recently gone into the text message settings and deleted the home number that was previously there. This was a phone that was given to me by someone and I didn't write down their number before I changed it. I now see that I can receive text messages but cannot send any. Can anyone lend a hand.. thank you

 

[B. Diddy]

Welcome to Android Central! Are you actually using their SIM card, or did you insert your own SIM card?