In cases of severe B12 deficiency/in patients with pernicious anemia or ileal disease, intramuscular B12 shots has been thought to be the only solution until a few years ago. Recent studies have shown that large amounts of oral/ublingual B12 can be effective treatment even in people with pernicious anemia, and promised (in some other thread) to post source for this info...
Here is a link to an article which states that oral vitamin B12 replacement is as effective as intramuscular injections, even in patients with pernicious anemia or ileal disease:
Vitamin B12 deficiency (from American Family Physician).
Here's another link to an article about the same topic:
Medical intelligence in Sweden. Vitamin B12: oral
compared with parenteral?
Some more links:
Vitamin B12 injections versus oral supplements. How much money could be saved by switching from injections to pills?
Oral vitamin B12 therapy in the primary care setting: a qualitative and quantitative study of patient perspectives.
Is Oral Vitamin B12 as Effective as Intramuscular Injection?