The question of whether they can ask these questions will be left to the trial judge. If the parties can make any kind of reasonable argument that consumers of one product or the other are likely to be partisans, the judge should allow the question, though it would not be error to refuse.
For a good comparison, look at Ham v. South Carolina, 409 U.S. 524, 525–29 (1973). There, the defendant argued he was framed for a petty drug charge because of his involvement in the Civil Rights movement. He thought jurors might be prejudiced against him because he was black and because he had a beard, but the trial court refused to let him ask jurors about either possibility. The Supreme Court said it was an error to refuse to ask the questions about race, but not about the beard:
The inquiry as to racial prejudice derives its constitutional stature from the firmly established precedent of Aldridge and the numerous state cases upon which it relied, and from a principal purpose as well as from the language of those who adopted the Fourteenth Amendment. The trial judge's refusal to inquire as to particular bias against beards, after his inquiries as to bias in general, does not reach the level of a constitutional violation.
Assuming the question is permitted, the mere fact of using an iPhone would not be sufficient to obtain a "for cause" strike, which the court will only grant if the juror does not indicate that he would be able to fairly consider the case. "I like my iPhone" is not enough. "I like iPhones better than Android" is not enough. "I hate Google" is not enough. "I worship at the altar of Steve Jobs" is not enough.
Instead, the question will be whether a juror indicates that they can set aside whatever prejudices they might have. The court is not required to strike them "as long as he or she ultimately asserts an ability to be fair and impartial." United States of America v. Abel Martinez-Salazar, 146 F.3d 653, 659 (9th Cir. 1998).
Batson prohibits peremptory strike based on "gender, ethnic origin, or race." United States v. Martinez-Salazar, 528 U.S. 304, 315 (2000). Other than that, a lawyer is generally free to strike based on anything or nothing at all (though there remain some questions about whether Batson also applies to other protected classes, such as sexual orientation, disability, age, etc.). So peremptory strikes would be the only permissible means of eliminating iPhone users from the jury.
