Depending upon the agency from which you are seeking funds, there are a variety of individuals who are willing to help you on your way to successful projects. Large federal agencies, such as the National Science Foundation, provide potential grant writers with one or two lead contacts and several other co-leads. Others, like the Department of Defense, may offer a technical lead and an administrative lead. On smaller state and regional grants, the same types of contacts as above may be offered, but you are more likely to see an anonymous email address where general questions/FAQs can be sent and posted on web pages for all potential summiteers to see.
There are various reasons why this recommendation isn't everyone's favorite. Since the conversation is live, there is the potential to insert one's foot-in-mouth and to be rejected outright. These are possibilities, but are certainly not the norm. To minimize the chances of such a conversation, it's best to set up a convenient time for a discussion rather than cold-calling a PD and hoping for the best. Better still, if allowed, send a one-page abstract to prepare the PD to help steer talking points if the conversation lags. If your idea is discouraged, it is likely not a direct reflection on you. Perhaps the solicitation was unclear in some aspect or the sponsor already had a specific type of project in mind. Rather than feeling slighted, view such an experience as a tremendous time saver and an opportunity to pursue the idea elsewhere or to develop it further.
A majority of the program directors who have spoken at RIT insist that personal contact be one of the initial steps to any project, since both the PI and the director benefit from this interaction: the PI gets name/face recognition and the director gets the advantage of having time to digest, mull and (depending on the agency) help cultivate an idea. If there is the option to discuss the project with an individual, do so in confidence. Sponsors are like any consumer with a set budget. They want the best quality that money can buy, and they have a fiduciary responsibility to their employing agency to choose wisely. When a PI submits a proposal without having made an initial contact, the chances of it getting a critical look are quite slim when compared to a proposal on which another PI has met and discussed his/her project with a sponsor. The latter is a surer investment.