Number sequences are used by beings [a type of being] who do not understand the English language, and are not in a position to do so since they are not "here", and have never had a "here" experience as a point of reference. This principle is demonstrated in the Roswell interview - at first the "vehicle" of the contact communicated telepathically in simple phrases but it was determined that the contact still had to learn how to understand English so that meaningful communication could be established. This is a primary reason for the existence of the device (the vehicle which housed the spirit energy of the entity) in the first place.
With regards to upcoming dates.
Dec 12 2012 = 4+4+4 (3 x 4 = 12), So the date in this way is 444 and 444 and 444
Dec 21 2012 = 7+7+7 (3 x 7 =21) So the date in this way is 444 and 777 and 444
3 is the multiplier / decoder / basic building block of your reality, known as "3D". [Added later]: In 5D you will notice sequences of "0's" and "5's." 000
and 555, 101010, 202020, and so forth. Decoding would be 111000, 222000.
This is only one of many ways to view this information.
These beings can influence electromagnetic devices since these devices are connected to the source field due to the device's nature as an electromagnetic device. Since human beings are also connected to this electromagnetic field, they can receive this information directly but there are many facets to communication which cannot be relayed through human concepts. This includes their (humans) ability and willingness to receive this information, as well as their (humans) freewill to do so. The greater the information is obfuscated the higher potential for freewill association. Can I give you one facet of a crystal? Of course not. When I give you a crystal, it is always composed of more than one dimension. And the human is equally acting on the reality and is a key component of the communication. This is demonstrated by noticing at a subconscious level that time is divided up into numbers such as 111, 222, 333, 1111, 1212, etc. It is never that "time" since this is a relative measure of distance traveled through space as observed from planet earth. Nobody else in the universe will have this perspective, since they do not have life on earth as a point of reference, although they might have a similar point of reference to their own experience. Another facet is that these are communications. As one approaches greater connection with the field he or she is also more susceptible to influencing their reality. This is the precursor/ first baby steps towards full conscious manifestation.
The decoding provided by Doreen Virtue is accurate inasmuch as the limitations of the communication can be facilitated, however these communications can be taken not as a separate entity but in context with other events in the "now" moment. A major part of this is the influence of the human on the NOW moment as intentional actions. Communications may have several different meanings, if only the radio was on at the time, for example, the message might take on different meaning since the communication is a multifaceted broadcast, and might have been intended to be taken in context with something else also happening at the time. Expanding one's understanding through free association can also yield fruitful results. Understanding that these are separations of the whole message or concept or idea. This is not inferior/superior but "limited" / single-faceted for the purposes of understanding the parts that make up the whole.
Crystal meditation is a means of facilitating multifaceted vision through a device that represents this concept. You may focus on one facet of what you are looking at or you may focus on all facets. This is the nature of the device. It is a representative / placeholder template for the act of seeing things in different ways. Those who understand the templated nature of reality, do not require the crystal device for meditation since they see the multiple aspects of reality at one time. But they may still use the crystal to facilitate/focus certain aspects of that meditation if they wish to do so. Some may wish to participate in a focused effort but variation is not an inferior concept. Some may fear making mistakes in their processes but in fact these are critical to survival of an idea, since these are variations of the idea. So the strength lies in millions of meditations which are and will be different because this is one of the natures of humanity, to explore the variances of creation. From an evolutionary point of view the same idea repeated is still just one idea.
And that meditation device may not be limited to a crystal - other devices may be used which reflect the template of the concept the meditation is intended to be realized. A mixing device (a spoon or spatula) might be held when the intent is to mix ideas into a pot of knowledge. Something with gears such as a watch might be used to gain greater understanding of the interconnectedness of ideas. A lens might be used for greater focus, or for taking a single snapshot of one's thoughts. A toy car might be used, for example to represent traveling in one's thoughts from one place to another. One should be careful of these devices since connections to these devices may carry unintended intent. Childhood and past life associations play a role in this. Where these exist, an intentional disassociation from the object is required.