Cell phone experts -- Can I activate a prepaid phone on my rate plan?

So basically, I’m a little naive.. and also impatient. I went out and bought a prepaid phone from someone for cheap. It’s brand new, unused, etc… I’m not at liberty to divulge further details.

Anyway, I got really happy thinking ‘wow! I bought a really cheap phone that I can now use with Bell! SWEET!’ But of course, as all things that are too good to be true, the phone won’t activate. Or at least, I’m not familiar enough with the process of activating.

So my question is: if I was sold this prepaid phone, can I still activate on my account even though I have a rate plan? The people at Bell are telling me this is impossible; others are telling me the people at Bell are full of shit