Most are Asian companies - the region produces eight of every 10 smartphones sold around the world - and operate in a complex legal, political and security landscape.
               
Only China's Huawei has publicly backed Apple CEO Tim Cook in his fight to resist demands to unlock an encrypted iPhone belonging to one of those who went on a shooting rampage in San Bernardino, California in December.
               
"We put a lot of investment into privacy, and security protection is key. It is very important for the consumer," Richard Yu, chief executive of Huawei's consumer business group, told reporters at the Mobile World Congress earlier this week.
               
But Yu stopped short of saying explicitly that Huawei would adopt the same stance. 'Some things the government requires from vendors we cannot do,' he said, citing an example of unlocking an encrypted Android device. 'These are important things for the consumer, for privacy protection.'
               
Lenovo Group CEO Yang Yuanqing declined to say whether he backs the Apple position, saying the issue required time and consideration.
               
"Today it happens to Apple, tomorrow it could happen to Lenovo mobile phones. So we must be very serious to consider. We need to take some time," Yang said.