After you’ve finished up with a two-year smartphone contract, one of the easiest ways to save money is to keep your old device and bring it to a compatible carrier with a lower monthly cost. But if your device is carrier locked — and if you bought it on contract from one of the big four carriers, it probably is — you’ll need to unlock it first. Last week Congress passed a bill that requires carriers to unlock eligible devices, although the carriers were already doing that voluntarily in some situations. President Obama still has to sign the bill, but he’s widely expected to do just that. So once it becomes officially legal, how do you go about unlocking your smartphone? Unlocking a phone from a wireless carrier isn’t an instantaneous process. Sometimes unlocking a device can take several phone calls and hours (up to two days, according to CTIA guidelines.)