Texts are really a crap method of communication if you're slightly paranoid. It depends on the other person having their phone on them, having it on, noticing that they've got the text and then deciding whether it's worth replying. My boyfriend always has his phone on silent, so if it's not in his pocket when it goes off, he won't notice until aaaaages after. If it's an important question then yes, it's annoying, but if it's really important I'd just call or e-mail (being a computer geek, he's a lot more likely to get the latter!)
Men are quite often naturally less communicative than women, and if it's only this that's worrying you and you're fine when you're together, I'd say it's just one of those minor flaws you get used to.