My experience with 4 different banks:

1. Limit of $500 cannot be changed

2. Limit raised to $1,100 over the phone; apparently if I show up at a branch and bring my first born, I can get it as high as $1,500.

3. Limit of $500 suddenly reduced to $200 (!) with the option to call in and raise it to $400.

4. Limit raised to $2,000. Some years later, suddenly reduced to $1,000. Haven't bothered looking into this yet.