As with other checks that are done by police, say, when they're stopping someone on the side of the road or conducting an investigation, there is a consideration of the immediacy of the situation. Some officers could have access through their cars. In other cases, detectives don't have that access. Many police vehicles do not contain the necessary technology, because often they are covert vehicles. But it only takes a phone call. Information is relayed to them within minutes.
On May 12th, 2009. See this statement in context.