Cheaper phones have less shielding and noisier circuitry. But if you test just about any device that puts out RF that close to any RD it'll probably go off.
All electronic devices have a small RFI field around them and things that transmit and receive have even bigger fields.
My CB radio will set off my whistler, haven't tried my rx65, but it has to be right by it. I also have a piece of crap Motorola i495 or 405 some crap that makes my monitor jump and speakers make noise when i get a call.