Almost any old smart phone, with or without a plan, can be used for Swagbucks and Perk. Lots of people (myself included) look for sales on really cheap pay-as-you go phones, but never sign up for a service plan. Most have a way to bypass activation and just use the phone connected via wifi. From late October to around Christmas, there were regularly phones for $10-15 that would run a variety of the SB and Perk apps. They would pay for themselves in a matter of weeks, too, so now I have a total of 10 devices - my current iPhone, my old iPhone, my wife's old iPhone, plus 7 cheap android phones, all 7 of which were between $10 and $15. They paid for themselves in less than 3 weeks and everything since has been pure profit.
I'm not saying there isn't some work involved, but more devices = more money for not much more work. Most of the phones run Perk all day, though - I only use 2 for SB, and when they're finished, I switch them over to Perk, too.