There are reportedly 70 cases in which federal prosecutors have invoked an All Writs Act, per court records from October.
The American Civil Liberties Union (ACLU) has compiled and released a map of the US detailing all the states where the US government is currently taking Google and Apple -and in some cases both of them - to court so as to compel both companies to unlock a suspect's phone.
According to Engadget, there are reportedly 70 cases in which federal prosecutors have invoked an All Writs Act, per court records from October.
Of that number, the ACLU managed to dig up 63 of them - nine of which targeted Google and the rest of trying to get at Apple.
You should note however that not all of these proceedings involve the same issue as the recent Apple-FBI court battle over the San Bernadino shooter's phone.
In some of the cases, the companies have complied with what the US government wants (the phones weren't encrypted or anything).
It should be noted as well that the FBI leveraged the All Writs Act, a statute it claims is used only as a last resort, in every single one of these cases.