Pokémon Diamond and Pearl/Solaceon Town

'''Solaceon Town is a small, out-of-the-way town you will encounter around the middle of your quest. Despite it being small, it is definitely not insignificant. There are several services here that you will probably use for the rest of the game.'''

Pokémon Day Care
In the northwest corner is the Day Care where you can drop off your Pokémon so they can level for a fee of $100 per level and if you leave two Pokémon that are compatible you can get an egg. For more details head to the Breeding section.

Inside after you drop off a Pokémon there will be a man who will give you the Day Care Checker Pokétch app

Newspaper Press
The house next to the Pokémon Center is the where the Sinnoh Newspaper is printed. Inside there is a guy who will tell you to bring a certain Pokémon within 24 hours. If you do so he will give you 3 of any type of Poké Ball excluding the master ball, cherish ball, heal ball, safari ball, and park ball.

Other things to do
Talk to the Ruin Maniac standing on the yellow path in the center of town. He will give you the Pokémon History App for your Pokétch, which shows you the last twelve Pokémon you have acquired.

Visit the home hidden by ledges in the eastern half of the town. The lady inside will give you a Seal Case. After speaking with her son in Solaceon Ruins, return to this house. If you have an Unown in the top slot of your roster, you will receive ten seals of the corresponding letter!

Once done in town then head into the Solaceon Ruins.