The "No Service" error may come up after the replacement. As others have mentioned, restarting the phone again is the best first step. Then reset the network settings if that fails. I tried to edit this into the guide but it got rejected. I've seen other guides missing software next steps as well and then have to dig through the comments or search elsewhere for a solution. Not sure why iFixit doesn't want software steps in the guides as it is an important step to a solution.
This was a really easy guide thanks. I had ordered a replacement DC in board but found after opening I could have probably repaired the existing one. It had been tripped over a few too many times. I think a bit of re-soldering on the connector where the tape covers in step 17 may have fixed mine. Now I have a backup at least.