Wireless distance confusion

We just put in a separate telephone line for DSL because we had conflicts with setting it up on our other lines. However, they would only run it to the first floor and both our offices are upstairs. The DSL jack comes out near the jack for a cordless phone. I read on this forum that a cordless phone could interfere with wirless signals.

There is another available jack inside a kitchen desk that is usually closed. I assume that this would also be a problem for a wireless signal to reach the second floor. Any suggestions?

GR_MIMI