Another version of the same thing - encrypt your phone with a large key file stored in memory (like an 8096-bit SSL private key or something). If you don't take some action (logging in, etc) every 30 minutes, the key file is deleted, rendering the data completely inaccessible.
You then have the option of keeping a backup version of the key file somewhere separate, where police aren't going to be able to find it or using a dead man's switch which triggers the destruction of the backup key on a longer timescale (1 day, 1 week).
Of course, encrypting the phone with a password whenever the screen goes off serves essentially the same purpose, the only difference being that using an auto-shredded key file would likely be slightly more convenient for day-to-day use, and that once the key file is shredded, it's impossible for them to compel the login information from you; the best they can do is get the location of the backup key from you, which can itself be booby-trapped to self-destruct (this has the advantage that it's stored on hardware YOU control, whereas a self-destruct password on the phone itself wouldn't do much if they bother to make a backup image before they start trying to decrypt it).
You then have the option of keeping a backup version of the key file somewhere separate, where police aren't going to be able to find it or using a dead man's switch which triggers the destruction of the backup key on a longer timescale (1 day, 1 week).
Of course, encrypting the phone with a password whenever the screen goes off serves essentially the same purpose, the only difference being that using an auto-shredded key file would likely be slightly more convenient for day-to-day use, and that once the key file is shredded, it's impossible for them to compel the login information from you; the best they can do is get the location of the backup key from you, which can itself be booby-trapped to self-destruct (this has the advantage that it's stored on hardware YOU control, whereas a self-destruct password on the phone itself wouldn't do much if they bother to make a backup image before they start trying to decrypt it).