Answer: The answer to this question is somewhat complicated. Firstlysome advice. Introducing anything into the cervix can possiblyresult in infection, a highly undesirable outcome. Should youdecide to proceed despite this risk, it is strongly advised thatanything you introduce to your cervix be squeaky clean.
Most women would find attempting what you are suggesting to beextremely uncomfortable, if not overly painful. At the very least,a great deal of time and patience would be required, as most womencan not just force an object of that size into their cervix. Of thepeople that have discussed succeeding, most if not all havementioned that they have had one or more vaginal childbirth.
Either way, if you truly are interested in pursuing this, a fingeris probably not the most ideal penetration to start off with(fingers tend to carry a lot of bacteria, and that fingernail ofyours is not going to be overly comfortable). Extremely small (andclean) vibrators or other smooth, thin devices can do the trick.For people who are very serious about pursuing this sort of "cervixplay", and do not have an overly accepting cervix, metal cervixdilators (similar to what doctors use, these can be found online),can be used in increasing diameter to gradually open the opening ofthe cervix to the point where other larger items (such as a finger)can be more easily inserted (the metal is easier to clean, neveruse glass as that can shatter). In two very unusual cases, I wasinformed that one woman was able to insert a small egg vibratorafter 3 hours of gradual dilation and another woman (who had aprolapsed uterus) was actually able to experience and apparentlyenjoy cervix sex. In the case of the egg vibrator, the woman had tostart if off slow, and if not enjoying sexual stimulation whileusing it, actually found it rather uncomfortable, though with sex,it was apparently very enjoyable.
Either way, expect cramping if you rush things along to rapidly,though again this may be different for each person.
Again, one last warning, foreign objects can carry bacteria, andthese can result in a very nasty infection. If you proceed and endup with any symptoms beyond cramps for a short period of time, youshould check in with your doctor to make sure nothing serious isgoing on.