Need some help, please

[* <3 I Love My HERO <3 *]

Before I get flamed for asking, I poked around the boarRAB and googled my question (to no avail).

I am planning on buying my BF a new phone. He uses Cricket, and refuses to switch to another carrier (I don't blame him). I've read that the new phone must be CDMA, but I am completely lost when I read about ESNs. I know I'll need to call Cricket with the ESN and his phone nuraber. Where do I find the ESN? What other information will Cricket need from me?

[AnnonO]

ESN nuraber stanRAB for electronic serial nuraber.
the majority of the time you can find it on the back of the phone.