When I was looking for some Arabic lyrics I was wondering why there are numbers inbetween letters in some words (eg. "Aw3a Tes2ny" or "7obak"). Is there a reason behind this?
The numbers represent Arabic letters of similar shapes, which mostly don't have an intuitive Roman equivalent: http://en.wikipedia.org/wiki/Arabic_chat_alphabet
For example, 7 is ح and 3 is ع, which represent [ħ] and [ʕ].
A similar phenomenon exists in transliterated Cyrillic, you sometimes see 4 being used for Ч; the similarity in shape is reinforced by the coincidental fact that the numeral "four" begins with that letter in all of the Cyrillic-using Slavic languages.
There are some arabic sounds that don't exist in English. We use numbers to express those sounds.
For example: In English, you use two characters together for expressing a specific sound such as "sh". But In arabic, we don't use two characters together. we use numbers instead.
To learn more about the pronunciation of these characters and sounds you can watch this video:https://www.youtube.com/watch?v=SPOA0sGx9Zo