Swallowing orally works. There are studies to show it works.

I don't think much is absorbed sublingually since the cobalamin molecule is so huge. It is dissolved in the saliva and swallowed.

What is important is to take on an empty stomach. Microgram quantities of any drug/supplement can be lost in stomach contents (esp fiber) and not be able to passively get thru the intestine. Now, this assumes you don't have intrinsic factor working properly and that is why you are low. Low or no intrinsic factor means the B12 has to cross the GI membranes passively and not hooked up to intrinsic factor. People with some or adequate intrinsic factor absorb more.

This link has pictures to explain it better:
http://www.aafp.org/afp/2003/0301/p979.html

Near the end of the paper is the data on oral forms working.

Remember, B12 is removed from the blood by transporters in the CNS. If the serum levels are low, then your spinal fluid becomes low, and there are studies showing MSers have low B12 in the CSF. The higher your serum reading, the better the transport into your CSF.

I think 1000mcg is best daily for average use. For people really low, 5000mcg daily is better. Methylcobalamin is best because many people lack the genetic capability to metabolize cyano (the synthetic form). This is called the MTHFR polymorphism failure and is quite common. Using the methyl form of B12 which is readily available now and inexpensive is the best way to go. Pennies a day... wish everything could be this affordable!