After completing the mission "Minisub" with Trevor I was supposed to receive a call from Wade telling me the Heist was ready. I did not receive the call and finished a ton of Strangers & Freaks.
A number of things to solve this:
- make a new save and delete the old save
- try phoning people as all three protagonists
- try sleeping a few times after each other
- Try fast traveling in a taxi.
If this doesn't help, you should probably reinstall the game or try again from an older save point