All I would really need is the basic minimum for calls/text and unlimited internet access.
That's the rub, though! Unlimited internet access costs. (I doubt it's included in the $40 plan, for example.)
Also remember that plans are per service provider rather than per device.
So for example I have Sprint for my Blackberry. Almost all of the major service providers (I'd guess all but I'm not sure) provide service for Blackberries. (Not so with iPhone, as Cycloptichorn referred to.)
Usually (not always) you choose a plan first, and then choose what device you want to use with that plan. (Blackberry, Droid, iPhone if available, or something else entirely...)