If it wasn't already clear, I'll restate what others have said in a different way. I will use demonstrative statements instead of questions.
Eigo ga hanasemasu = means to be able to speak English
Eigo wo (o) hanashimasu means to speak English, that is, to use English to communicate.
For example, when i talk with my friends from Japan, we use English.
Ni hon jin no tomodachi to shaberu toki, watashitachi ha (wa) eigo wo (o) hanashimasu.
This is what my friend told me.
My Japanese isn't perfect, so maybe someone can verify :)