Since you mention "infant" in the question, the most relevant systematic review I was able to find, is "Effectiveness of treatments for infantile colic: systematic review" BMJ 1998;316:1563
This evaluates 27 clinical trials, and among the conclusions are:
No benefit was shown for simethicone
It should be noted that "infant colic" refers to babies crying, or showing symptoms of distress, for no discernible reason -- since they can't talk, we don't know where their pain is. It could be a headache, in which case gut treatments aren't going to help.
In adults, Holtmann, G., Gschossmann, J., Mayr, P. and Talley, N. J. (2002), A randomized placebo-controlled trial of simethicone and cisapride for the treatment of patients with functional dyspepsia. Alimentary Pharmacology & Therapeutics, 16: 1641–1648. doi: 10.1046/j.1365-2036.2002.01322.x
Simethicone and cisapride were significantly better than placebo for symptom control in patients with functional dyspepsia after 2, 4 and 8 weeks of treatment. Simethicone was also superior to the prokinetic cisapride in the first 2 weeks of treatment.
This study is funded by Asche AG, and you have asked for studies "not funded by the vendor".
Drugs.com (credible with good onward referencing) states that simethicone is effective for flatulence, functional gastric bloating, and postoperative gas pain; "not recommended" for infant colic, and that its efficacy has not been demonstrated for intestinal distress and "immediate post-prandial upper abdominal distress".
So my conclusion is that simethicone is effective at relieving trapped gas in the adult gut, but that trapped gas in the gut is not typically the cause of baby colic.