"I promise I'll write to you as soon as I arrive, Jane," said Nick.

• Nick promised Jane that he will write to her as soon as he arrives.
• Nick promised Jane that he would write to her as soon as he arrives.
• Nick promised Jane that he would write to her as soon as he arrived.
• Nick promised Jane that he would write to her as soon as he would arrive.
• Nick promised Jane that he would write to her as soon as he will arrive.
• Nick promised Jane that he wrote to her as soon as he arrived.