Coming a little out of the blue, it seems that an LTE version of Asus' Transformer Pad TF300 is 100% real and is to be released in Europe this month. A German press release issued today indicates that Germany and Austria will be seeing the TF300 LTE in the middle of August. That's pretty close to now.
Available in red and blue in both countries, a white version can be had only on O2 and without the docking keyboard. Prices without the keyboard are set to be €529 ($651), and with the keyboard €629 (about $774). It's a little pricey, especially given the other Asus tablets available. But, it's got LTE and for some that's enough to warrant parting with their hard earned. There is no mention of prospective availability outside of these two countries at the moment.
Prospective German and Austrian buyers should be sure to check out our full review of the WiFi only TF300.