New mobile customer

Have a question about the cell phones offered on the comcast site.  Can I buy one of those phones being offered at another retailer, will it work on comcasts network?   I understand it needs to have an IMIE number that comcasts approves of.  Do they have the phones online made for them, so I would need to buy the offered phones on comcasts site?

Im not tec savvy so please be gental.  I only want a talk text phone, no need for data.

Thank you

Rabbab