This is a rare case on the Electronics site where, none of the answers clearly and crisply answered the question!
Do cellphones retain the ability to detect tilt in zero-gravity conditions?
The answer is:
#They retain (at a hardware level) the ability to detecting tilting, but they can no longer detect tilt.
Further,
At the level of app software, in fact, almost all (very likely "all") app-software-writers would not allow for the corner case of zero-gravity, so very likely the gyro-accel functions would act whackily overall, in most/all actual apps.
Regarding how gyros/accels work in phones, you can easily google the APIs for these on the two platforms. Example,
Note however that all OSs as of writing, in practice wrap the lower-level gyro/accel functions in some sort of convenient higher-level motion manager:
#Accels/gyros, in fact wrapped together at the OS level: https://developer.apple.com/reference/coremotion/cmmotionmanager
So in fact...
in practice, for any fairly newly-written app (remembering that, let's say, about 25% of apps in the store are decayed / not updated regularly), it would come down to how the team at Apple which wrote (in their case) "Coremotion" handled (if at all!) the zero gravity environment case. (There's a similar situation for droid.)
And further, for games as such...
Today almost any game you pick up and play on a phone was created in Unity3D, rather than as a native app. (And as a rule, if you look at the set of "apps which use the accel/gyros", 90% (more?) of them are just games.) So in fact (on all platforms) the software-writers are actually using's Unity's level of software wrappers.
(To wit, https://docs.unity3d.com/ScriptReference/Gyroscope.html etc)
Hence, the actual behavior in the extreme corner case of earth orbit, would depend on what those folks did when writing that.
#One confusing point...
that hasn't been clarified. When you're writing software for phones, it's totally commonplace to have to deal with "zero gravity" ... for short periods of time: that is, when the phone is in free-fall. (So if you're making one of the (100s of) apps for skateboarders, skiers or the like which measures hang-time and so on, you deal with this as a matter of course.)
http://www.livescience.com/40103-accelerometer-vs-gyroscope.html
By the way, gyros were introduced to phones about 2010; accels were in them from the start.
A French/Italian company called STMicroelectronics pretty much makes most of the gyros for both apple and samsung.
Regarding accelerometers, most phones now have a couple of them since it works better that way. I have heard that there is more variety of suppliers of accelerometers (Bosch, etc).
You can literally buy MEMS gyros or accels somewhere like this,
buy yourself a few thousand MEMS chips
if for example you are making an electronic toy that includes such a feature.
Regarding literally how MEMS accelerometers actually work at a substrate level, google things like http://www.instrumentationtoday.com/mems-accelerometer/2011/08/
Regarding MEMS gyros, http://electroiq.com/blog/2010/11/introduction-to-mems-gyroscopes/
Just to repeat, the fundamental quick answer to the question posed is
#In "zero g", they retain (at a hardware level) the ability to detecting tilting, but they can no longer detect tilt.
In terms of the software,
A - it would, almost certainly, "totally fail!" in the whacky "you're in orbit" case. Since no gane or app engineer (I know) would be so OCD as to cover that case, but don't forget...
B - it's totally commonplace to have "zero gravity" .. during short periods of freefall (this applies as a commonplace matter if you're making one of those "action sports apps").