I just watched the Titan hands on video and there was a H in the top left corner of the screen. That's AT&T's indication for non LTE "4G". It actually means HSPA+ which is definitely faster than 3G but not quite LTE speeds. AT&T only just today launched their first LTE phones and sadly those are Android phones.
I am in the NYC area if that matters, not sure if it is available everywhere.
The Titan will "theoretically" bring 4G speeds with HSPA+. NYC does have HSPA+, but currently does not have LTE. AT&T stated that they were bringing LTE to NYC in the near future, but wouldn't effect Windows Phone users as no current device (including the Titan) will be capable of running on LTE.
Here is what you really need to know: Yes the Titan will have 4G as in HSPA+, and no it doesn't really matter if you have LTE or not. The truth of the matter is LTE will be offered in such a limited market right now that it won't really be "widely available" until your 2 year contract is up and you're ready to get your next phone. AT&T's HSPA+ network a year from now is going to look like their 3G map now, basically it's going to cover more areas. Also, the trade-off with LTE is poor battery life.