I'm not 100% sure, but I think you can get any phone in what they call "Unlocked". I believe this means that you can use it with any carrier, but that still may not be the case with a prepaid carrier. Would be something to check into if you "have" to have a specific phone to fit your likes or needs.
Around here there are tons of shady shops that will happily unlock any perpaid simlocked phone for a couple of euro's. Best thing of all is that you don't breach any contract whatsover, since you didn't sign any contract in the first place. Completely legal. My last prepaid phone had its simlock removed within 30 minutes of purchase.
Use any unlocked phone that is able to use the network of the provider of choice (99% of current phones are) and buy the SIM card.
Get a bundle of phone and SIM. The phone is somewhat sponsored, thus locked to the SIM or provider. After 24 months, you can request an unlock code from the provider for free, if you don't want to wait that long, you have to pay 100 Euro (140 USD) for the unlock code.
Additionally, most phones that are bundled with prepaid contracts are basic models, so such a bundle isn't a very attractive option, IMO.
Same around here, but it can still be legal to have your simlocked subscription phone unlocked in said shady shops. Depends on the contract.
In addition to that, it can also be very very beneficial if you can change the IMEI number if you never want ot be traced. Because your a mob member or just very paranoid on privacy. If you can connect to a network with a completely random IMEI number, that would be very awesome!