Calling hogs from a mile would be pretty cool. That would be tough. You certainly can call them from out of the brush, but you can call them in from much farther as well. You can call them from a half mile away as well. I can't find Glenn's video that shows calling from a good bit farther.
That you
can call them from long range does not seem to be the norm, however. Also, choose the wrong sounds and instead of calling hogs, you can literally drive them away.
Glenn does have the best calls. The Covergent bullet is pretty nifty and works at longer distance than most blue tooth speakers, but the only problem is that it is line of sight, meaning your phone with the app needs to be in line of sight of the speaker or you may lose connection. Convergent has a picatinny mount so that you can keep your phone out and on your rifle, so that your phone stays in line of sight with the Bullet. For example, you have the bullet set up at 70 yards and you get your call going and drop your phone in your pocket and PRESTO, no more call coming from the speaker. If you are hunting in the day time, having your phone out probably isn't a problem in regard to being lit up. If you are hunting at night, having your phone out certainly may be an issue because of back lighting.
Most bluetooth speakers won't get you beyond about 30 yards. I suspect that the Bullet has a range extender built in to it that other bluetooth speakers don't have, which is what makes it special.
Oh, and be sure to turn put your phone into airplane mode or otherwise it is a real shocking surprise to hear your phone ringing from the middle of the field when a call comes in...