[Windows Phone 8 Development and Hacking] GoodDayToDie:
Questions and Answers

Can I install WP7 interop apps using this?

They will install, but there's no point. They almost certainly won't actually work. Interop-unlock enables access to parts of the OS which third-party developers were not intended to touch; consequently, there's no backward compatibility. Even the methods used for native code on WP7 (which is different from, but nearly essential to make use of, interop-unlock) won't work on WP8. However, it should be possible to port many of those applications to WP8.

Will this work on Lumia phones / How can I get this on my Lumia / Are you working on this for Lumia phones / What about HTC, or some other OEM?

The current hack relies on a Samsung-specific component. Adding support for other phones will require new hacks. We are looking into it, rest assured; at this time, however, there is no way to gain interop-unlock on any WP8 device other than a Samsung one.

EDIT: It looks like there should soon be a Huawei W1 custom ROM with interop-unlock included. I don't deal with custom ROMs, but you may be able to use homebrew apps on that phone too.

EDIT: Lumia phones *can* be interop-unlocked via JTAG. However, this requires some extra hardware and some phone disassembly. Not an online hack, and not for the faint of heart.

But what if we installed the Diagnosis app on a Lumia phone (using Fiddler proxy or similar) and then followed this guide?

I repeat, Samsung-specific component. Nokia doesn't put the required services/drivers for Samsung's Diagnosis app into their Lumia firmware, so the app would not work!

Can I upgrade my phone to GDR3 if I have this?

Yes. However, be aware: if you install Samsung's updates that come with the retail GDR3 update, it will break your ability to re-unlock, or to use some homebrew apps! (Developer preview updates are fine, as those are purely Microsoft code and don't mess with the Samsung components.)

EDIT: There's a way to unlock the Samsung services for full access again on GDR3. You still need to interop-unlock beforehand, though.

Can I re-lock my phone if I want to?

Yes, easily. The simplest method is to use the Windows Phone Developer Registration tool (the one that comes with the SDK) to de-register the phone (you can then re-register it if you want to get your normal dev-unlock back). This doesn't remove any changes that were made using the interop-unlock, though (for example, it won't undo the EnableAllSideloading hack, not will it set back the Full FS Access hack). Apps that require interop-unlock will still be installed, but may no longer run. To manually remove interop-unlock, you can reset all the registry values that were changed by the interop-unlock hack to their original values, and remove all the apps. There still may be a great many other changes that also need reverting, though, if you want to get back to stock settings. See next question.

Can I get my phone completely back to stock settings without knowing every little thing I changed?

Yes, a hard (factory) reset will undo all changes made by interop-unlock, or any apps (including ones that require interop-unlock), and will remove all apps. If you need to send your phone in for warranty servicing and are worried that they won't take it because you interop-unlocked it, this approach will fix that (they would probably tell you to hard-reset anyhow, if it's conceivably a software problem).

Will the interop-unlock survive a hard reset?

Not using this method! Read the question above. This unlock is purely in software, not firmware; it is reset along with everything else.

Can I upgrade my phone to WP8.1 if I have this?

Tentatively, yes! We're still working on figuring out exactly what WP8.1 means for the homebrew scene. The short version is that most apps and some (but not all) of the hacks they contain seem to still work, though. However, see next question...

Can I interop-unlock my phone on WP8.1?

At this time, I don't believe this is possible (unless you can use a custom ROM). One step of the process appears to have been "fixed" and we will need to find a different way. -W_O_L_F- has indicated that he has one, possibly coming soon...