Yunho might be awaiting Siwon with open arms!  He is already in the military while the latter is about to be enlisted.

Siwon posted on his Instagram a personally written letter he received from his SM senior on November 17.  He wrote, "The present from Soldier Yun with great sense.  Thank you." 

The handwritten letter reads, "Siwon, write often.  Always be happy and write well when you're in the army.  I bought this with my own money.  Congratulations on becoming a soldier.  Also, I enjoyed your drama. Amazing."