For all the info you will ever need to watch any preseason NBA game, whether it be on your television or through a streaming device, continue below. This entry is broken down into: TV viewing options and online streaming options, to make it easy.
TV Viewing Options
NBA TV, TNT, ESPN
NBA Preseason - National TV Schedule
As you can see from the above link, most every NBA preseason game will air exclusively on the NBA TV channel. Check with your cable/satellite provider to see if you get the channel. Keep in mind that most basic cable packages won't offer the channel in their bundle initially, so it will likely be an extra charge. Likely reasonable addition though.
To see what channel your provider airs NBA TV, or to see if your provider offers it, use -- NBA TV Providers list.
TNT and ESPN will also be airing a few preseason games as well, once we start to get close to the regular season. Again, use the NBA Preseason TV schedule above to see which games air where.
Online Streaming Options
NBA League Pass, Watch TNT, Watch ESPN
NBA League Pass is the best place to watch any NBA preseason game, but it's not the cheapest.
Full access will run you $199.99. Keep in mind that is only a one-time charge though. And it's a little better than it sounds. First off, you can make 5 payments of $44.99, and it also gives you access to all the regular season NBA games as well (that aren't already nationally airing in your area). And their on demand feature makes all games available to watch, just 3 hours after any game airs. And for those just looking to follow one particular team, they offer a discounted $119.99 rate.
On top of that, you also get NBA League Pass Audio, so you can listen to all NBA games live. And if you just want the radio option, that is far cheaper as a stand alone service; something I would highly recommend for just a one time fee of $9.99.
TNT and ESPN will be airing a few preseason games as well, and you can access them on your mobile device or PC by going to their respective sites, and using your login info for live game streaming.
Hope this helps. Enjoy the NBA preseason!