iPhone sending txt

hi all im new to all this iphone stuff so pls go easy on me.
well i just bought it off my mate unlocked so have put my tmoblie sim in and want to send txts but keeps saying error? i can send them ok.
also how do i get the games on and do i need any software?
many thanks
big-ron

Have u selected which network u are on ? it might be set on your mates provider

settings -> carrier

HTH

nilrem said:

Have u selected which network u are on ? it might be set on your mates provider

settings -> carrier

HTH

Click to expand...

hia I can't seem to see this setting on the one I have?
(carrier)
many thanks

r u sure it's definately unlocked ?

press the home button then settings and carrier should be 3rd option down under aeroplane mode and wi-fi

ok yes found it. got it on TMO UK but still saying error sending message?
sorry to be a pain