Okay does he want me to call him?

Okay there is this guy i know and am friends with and he gave me his # but i have at&t and the # was verison,(and I don't have very many minutes, and no texting) so i never called him (and plus i really didn't wanna) so he evidently had another phone that is at&t and then the next week he asked me if i got the e-mail (when he gave me the at&t #)i said yeah sorry i didn' call. So he keeps asking me and I just tell him ive been busy (wich is very true!) but the problem is...i really like his brother. so what should I do?