Having read the following text from the Road Traffict Act I would plead not-guilty anyway as the law says you cannot "drive" and you were stationary.
1. No person shall drive a motor vehicle on a road if he is using -
- 1. a hand-held mobile telephone; or
- 2. a hand-held device of a kind specified in paragraph (4).
4. A device referred to in paragraphs (1)(b), (2)(b) and (3)(b) is a device, other than a two-way radio, which performs an interactive communication function by transmitting and receiving data.