It is allowed by 820.52(A)1(c)exception #1, and simularly for phone and data by 800.52(A)1(c)exception #1.
Simular to what is shown in the top right coner of this catalog
http://www.carlon.com/Brochures/Master_Catalog.pdf For metal boxes youre limited to the use of a extra capacity box with a divder card.
Will it cause interferance, not really, nothing noticable anyway.