In previous games, to get rematches with trainers, you used the VS Seeker to see if the trainers were willing to battle. In HeartGold & SoulSilver however, the rematches are done a different way. Firstly, only a few dozen trainers in Kanto & Johto are capable of being battled again.

In order to get the rematch, you have to receive the PokéGear number from the trainer in question. Then, on a certain day, you will need to ring the trainer in question to organise a rematch. It is not guaranteed that a rematch will be discussed when you call but keep trying and you should get it. Below is a list of all the trainers, battleable on Sunday, and their teams including their first team and each team's increase in level. Click the other days to go to their page

Monday | Tuesday | Wednesday | Thursday | Friday | Saturday | Sunday

Sunday

Time	Location	Trainer
Morning 4am-10am	Johto - National Park	Lass Krise
Teams First Battle Lass Krise Oddish Cubone Level 14 Level 17 Second Battle Lass Krise Oddish Cubone Level 21 Level 31 Third Battle Lass Krise Gloom Marowak Level 32 Level 38 Fourth Battle Lass Krise Vileplume Marowak Level 53 Level 54
Morning 4am-10am	Kanto - Route 27	Ace Trainer Reena
Teams First Battle Ace Trainer Reena Growlithe Nidorina Staryu Level 36 Level 33 Level 36 Second Battle Ace Trainer Reena Growlithe Nidorina Staryu Level 38 Level 36 Level 38 Third Battle Ace Trainer Reena Arcanine Nidoqueen Starmie Level 47 Level 43 Level 47 Fourth Battle Ace Trainer Reena Arcanine Nidoqueen Starmie Level 54 Level 53 Level 56
Day 10am-8pm	Johto - Route 34	Picnicker Gina
Teams First Battle Picnicker Gina Hoppip Hoppip Bulbasaur Level 9 Level 9 Level 12 Second Battle Picnicker Gina Hoppip Hoppip Ivysaur Level 24 Level 24 Level 32 Third Battle Picnicker Gina Skiploom Skiploom Ivysaur Level 26 Level 26 Level 44 Fourth Battle Picnicker Gina Skiploom Jumpluff Venusaur Level 30 Level 36 Level 55
Day 10am-8pm	Johto - Route 42	Fisherman Tully
Teams First Battle Fisherman Tully Qwilfish Level 11 Second Battle Fisherman Tully Qwilfish Level 33 Third Battle Fisherman Tully Goldeen Goldeen Qwilfish Level 30 Level 30 Level 38 Fourth Battle Fisherman Tully Seaking Seaking Qwilfish Level 41 Level 50 Level 53
Day 10am-8pm	Kanto - Route 17	Biker Ernest
Teams First Battle Biker Ernest Teddiursa Marill Level 45 Level 44 Second Battle Biker Ernest Teddiursa Azumarill Level 46 Level 47 Third Battle Biker Ernest Teddiursa Azumarill Level 48 Level 49 Fourth Battle Biker Ernest Ursaring Azumarill Level 58 Level 54
Night 8pm-5am	Kanto - Route 17	Biker Reese
Teams First Battle Biker Reese Weezing Level 45 Second Battle Biker Reese Arbok Weezing Level 42 Level 48 Third Battle Biker Reese Arbok Weezing Level 48 Level 50 Fourth Battle Biker Reese Arbok Weezing Level 56 Level 55