You should be specializing in translation, regardless of the format you work for. And I'm pretty sure you can find a cheap Android phone around to test if things work right.
My partner already does "specialise" in translation. She does freelancing for a living. I simply had the theory that it'd be more effective to niche down, and I chose to target iOS because: I'm a user of iOS, I have some iOS development experience, and the App Store is growing in Japan. We're not basing our livelihoods on the decision. It's just something we're testing.
