Note of greetingth

A friend of mine thent me thith note. He’th a little bit thy and often preferth to thend a metthage rather than thay thomething in perthon, even if it’th quite thort, and thometimeth amutheth himthelf by putting it in the form of a putthle. I honethtly have no idea what to make of thith one though, although from what he thaid when he gave it to me, I think one of the lineth on the left ith encrypted quite thimply, uthing a different technique to the otherth. I’ve pothted it here, in cathe any of the brilliant putthlerth on thith thite can help me with it. What ith he trying to thay?

Edit: Sincere apologies, there was a slight error in the original image. I’ve updated the image. It will not change the solution; there was a word misspelled at one point – you could certainly solve the puzzle using the original image, and if anyone is partway through the solution, they should be able easily to modify it. The corrected text can be found here.

Hint: I’m not sure whether anyone’s working on this, and if so where they’re stuck, so I’ll begin with a basic hint in case anyone wants to give it a crack…

Feel free to post partial answers, as there’s a few little steps to this puzzle.

Hint 2: Since there was some interest in this puzzle, but there’s been no progress in about a month, I thought I’d post a little hint in case anyone is still interested…