Last fall, Microsoft execs said to expect an LTE-enabled Surface 2 to debut on AT&T and Vodafone. They made it clear at that time that it would be an ARM-based device, not an Intel-based one, that would get LTE wireless connectivity. Nokia's Lumia 2520 ARM-based tablet already has LTE support and is available on Verizon and AT&T both.
Microsoft officals recently declined to comment on when the promised LTE-enabled Surface 2 would be available.
Microsoft also is still believed to be readying a Surface mini-tablet with a screen size between 7 and 8 inches. Last I heard from my sources (last year), the target date for availability of the Mini was spring 2014. There's no word, at least from my contacts, as to whether the Surface Mini will be LTE-enabled. I had heard Microsoft was planning to make ARM the processor inside the Surface Mini, but others have reported that they believe the device will be Intel-based.