Two children have taken their battle against phone masts near where they live to the Court of Appeal.
Phoebe St Leger-Davey, six and James Harrison, seven, want the court to have another look at the decision to allow a mast close to their Winchester homes.
Some people are worried the masts give off radiation dangerous to children.
The hearing might influence 12,000 other similar cases, including one against a mast near three schools in Harrogate, Yorkshire, on Friday.
The radiation that the masts give off is below international guidelines.
But the law says people's fears about health should be thought about when putting new masts up.
The children's lawyers say that means the decision should be reconsidered.