Texting has become the most used form of communication nowadays so you gotta know what your doing. BBM (blackberry messenger) is excellent to talk to girls with, its instant, it takes away the girls nervousness that calling brings and you can tell if they read your message =P, consider getting a blackberry simply for this, it opens a social network and if someone wont give you a number, they'll probably give you their BBM.
When messaging, be short and to the point. Tell the girl what you want, be confident. Dont be bitchmade / uberrespectful. ex. "Maybe if you would like to come you could try" type of shit. Thats a wimp talking, try this = "You should come out, I need a lady to cuddle with later" still somewhat innocent but you getting the point across. (also depends on how much the girl is feelin you and what kind of a vibe you gave off when you met her).
A huge point in all this is PATIENCE. Dont be talking your ass off, if you say something you wait for her reply no matter how long it takes, if it never comes she wasn't feelin you and you go get another girl. Dont waste your time asking a million questions, tell her what you want and she'll either do it or she won't.
Dont change plans for a girl. If you say come meet me here and she instead says go meet here there, dont budge, tell her nevermind then. Stay in charge and wait it out, she'll come and you will gain respect, chances are you lose it if you go. (Obviously if you live in sum shit apartment n she got a fat house n hot tub get your ass over there)
A good sign is when girls start texting you first after receiving a number, this means they are interested and your game plan is workin out for you ;), if you are at this point keep doin what your doing.