This is a very interesting topic because while the reader would like to think that because Austen is criticizing the social class structure in England that is possible it will change, but in reality, it cannot. The social class stratifications are so entrenched that nothing is really changed by the end of the novel. A reader could look at Elizabeth and note that she "married up" in social class, and that is true, but she wasn't "upwardly mobile" by any means other than marriage and her status is based entirely on her married name, not anything of her true self.
A key element of this novel is the theme of marriage and the satire on the necessity of women to marry in order to avoid abject poverty. If women MUST marry to survive then there is no social mobility. Everything a person is in society is based on his or her family connections or on the connections to the upper classes. Collins is just a middle class minister, but his connections to Lady Catherine make him more important than he might otherwise be. On his own, he isn't likely to rise to any real status in the church. Wickham is the lowly son of servant, and the only reason he has any wealth or his position in the army is because of his connection to Darcy -- first in his original benefits and later in his acceptance of the settlement for marrying Lydia.