If you happen to be a mobile customer of O2 in the UK, then it's possible to participate in the upcoming multiplayer beta for Call of Duty: Black Ops 3 just by using the O2 priority app.
Thanks to VG247 for the photo
Many have reported that they haven't been able to receive a code, and there definitely is a count-down for a fixed number, though that's been said to refresh on a daily basis. So if you really want to get in on the beta but don't want to pre-order (and you're an O2 customer), then download the app and commence waiting until the refresh, these seem to be hot ticket items.
Call of Duty: Black Ops 3’s beta starts on the 16th August for the PS4 and on August 26th for the Xbox One and the PC. If you haven’t, it’s of course available for pre-order right here. It’s being developed for the PlayStation 4, Xbox One and PC and will release on November 6 2015.