[SkyMarshal]

Well, technically there's a 'ch' sound in aitch, so it sort of includes its own sound.

[duke_sam]

Also in some parts of the world there is a leading H sound, specifically Ireland.

We also pronounce R like 'or' instead of 'are' which causes endless amusement every time I use the abbreviation HR in the states.

[a1k0n]

In some accents it's pronounced "haitch".