Who said anything about the phone? Where in my post did I say anything about talking on the phone?
Frankly, I don't see why you are offended. If you NEVER want to talk to human beings in person or on the phone, and think that's okay, then that's your right. However, you say texting works for you and if that's what you wish to do the rest of your life, well, good luck finding and keeping people in your life who will go along with it.
A conversation can easily be had via text, which is what this thread is about.
Personally, I dislike texting on my phone because it's awkward and I don't have a text messaging plan which makes it expensive. I do, however, pretty much communicate with most of my friends exclusively through text - just not phone based text messaging. We're spread pretty far over the country now and none of us could afford to be that talkative over long distance phone call rates, but even when we were in shouting distance of each other's dorms we still used IM instead of the phone to get multiple people in one conversation at a time without having to seriously interrupt schoolwork to do so.
That said, one of my inlaws will only communicate via text messages on his phone, even when we're meeting in person. He's deaf, and texting is how he can talk to me even though I don't know sign language. He owns a tech company and we've a lot of interests in common that I would never be able to know about if I stuck to verbal communication as some kind of gold standard. It's awesome that we are still able to communicate, and I am ever thankful for the technology that allows it.
It sounds like OP is looking at text messaging as more of an instant messaging type thing. When I IM a friend, I know they're online, can see that they're available, and on some chat clients can even see when my messages have been marked as read. So in that case it's to be expected that people will answer back quickly because you can see that they're there. IM conversations tend to start and stop and jump back erratically, but then internet connections can be fickle, and a person can't sit at a computer all the time, so that's just the nature of the beast.
Texting, on a phone, is more like email. You can't see if the other person is available, or even has their phone on. The message gets to them when it gets to them, so you've got to just be patient waiting on a response. It's possible that OP's buddy isn't really entirely considering it like an IM, but more like a speedy email, while still using the IM type conventions of BRB to say that he's AFK for a while. His lingo isn't so much matching his usage, but like PP's have said, it's just an incompatibility of texting styles going on, not something really rude.