I've deliberated this one for awhile and tested both ways. I'm still of the belief that asking a girl for her schedule is the
optimal way of getting dates.
There's more than a few things other than just "leading" that needs to be taken into account. The first thing is that "leading" over text message has
very little effect as opposed to leading in person. It's a lot easier for a guy to command a girl to do something over text message than it is for him to do it in front of a girl's face, with solid fundamentals. When a girl sees a guy telling her to do something over text, it comes across more as "demanding" than it does "commanding." Also, I always follow my own rule that
extra effort given over the phone is more often chasing and extra effort in person is more often persistence.
The best thing you can do by phone is simply not beat around the bush, and be warm. Within a few text messages, you should be attempting to set up a date or a girl will lose interest. The reason I choose to ask a girl for her schedule is that it follows
the path of least resistance -- she selects what's best for her rather than being forced to accept a time that isn't ideal. It's a lot more likely that you'll attempt to "push" for a date at a specific time and get resistance because she might just genuinely be busy at that time... which breaks down the flow of the momentum when she has to respond with, "I'm busy

." Suddenly her emotions take a slight drop, even though they were rising from the moment she met you. From a guy's perspective, this may not seem like much (logically), but for a girl, she suddenly loses some momentum in her feelings (emotionally).
Me: Hey HB, we should grab that frozen yogurt soon. When are you free this week?
HB: I'm working and have school all week. (Ugh! Too much thought and planning required of her)
The response in the above message sounds less like a rejection of your text and more of a rejection of
you. If she was interested in getting together with you, she would give you the days she wants to see you, or she would at least suggest trying again another time. Also, the "warmth" comes from using emojis/emoticons. I still don't understand why some people don't use them when they see guys like me, NJ, and Richard (T Vaunswa) using them in all of our interactions. Tone is
very important, and emoticons shows that you're socially savvy and warm.
Me: Hey HB, let's meet up on Thursday at 3:00. Let me know if that works for you.
HB: I'm working at that time... are you free any other time?
or
HB: I made plans already
Me: Not a problem, but you're making it up to me then

HB: Ok I"m free on Wednesday lol
This is essentially you still asking for her schedule, but you're having to do it in 5 text messages rather than 2. And I won't always rely on a girl just throwing out a date when you don't directly ask for it. The text back from her throwing you a specific day (Wednesday) seems very unlikely (unless she's very into you, in which case it doesn't matter what approach you took) unless your last text to her was restructured more like this:
Me: Not a problem... so what day are you free then?

HB: I'm free Wednesday!
But again, you're just asking her for her schedule, which could have been done earlier in the conversation.
A rule of thumb:
every extra text past the first few necessary to set up the date decreases your chance of the date actually happening. You always want to minimize the possibility of her deciding that she doesn't want to engage in the interaction anymore and suddenly stop texting you.
The last thing I'd like to mention is that the
real discrepancy between the two methods here that will have more of an impact than anything else is
how clear and direct your invitation is. Without using the word "date," the girl needs to feel like that's exactly what you want. If your text looks like this:
Me: Hey HB, when are you free next week?
or this...
Me: Hey HB, let's kick it next week. What are you up to?
...or anything else ambiguous, then you're a lot more likely to get flaked on. Make sure she knows what you want, and if your approach was good, you'll get the response you were looking for. =)
- Franco