About a month ago Transport for London launched a new number for their Travel Information Call Centre. It is 0843 222 1234 which is reassuringly similar to the old number (020 7222 1234).
Just be aware that this number may not be included in your 'free local call' quota if you have such a thing in your landline or mobile package. If you were previously calling from within London (or from just outside), then the old '020 ' would have been included in most quotas.
The old number is still working.
Thanks to London Reconnections for the tip (and see for more detail).