Thank you for responding.Since posting my message, I've reread the few post-it size notes I received from Ntl Hdqs and really explored the internet for info, plus I received an email from Lynn G that helped me understand military language.
Dad was apparently first assigned to Co L 311th Reg 78th Infantry at Camp Butner, NC where he trained, and his military occupational specialty was telephone switchboard operator 650. First dental note was for April 1944 and he was with the 78th at that time. The handwriting on the slips (by medic)is hard to decipher and it is 3217 Signal Service Battalion and that was March 15,1945 at the 7th General Dispensary.
But, the confusing part is he was with Co L, Reg 175, 29th infantry when he departed the states for Europe on May 12, 1944 and he was injured by the mortar shell while with the 29th on March 23, 1945, but as stated above was shown by medic as 3217 Sign Serv. I finally deciphered the hand writing to say "hit by mortar shell while on walkie talkie" near Brest with injuries to arms, legs, skull and possibly internal abdomen - removed protruding shrapnel and xrays of all ordered.No further notes on treatment available.The 3217th Serv Corp must have been part of the 29th.And, from other info, it's clear he was also infantry.I guess he had to be the radio guy and combat, too.
From other message boards, I gather that radio guys were in short supply - one post saying 8 guys were transferred from his regiment to others for overseas.
In looking at his picture, taken at NC while 78th, his shoulder patch is that shown on the net as a Service patch.But papers say assigned to infantry, and he got the expert rifle and the Combat Infantry and the other medals previously mentioned and took the rifle fire at Omaha Beach.