You can certainly carry magazines in improvised pouches satisfactorily and discreetly, but purpose built mag pouches have alot of advantages that are hard to discount. A purpose built single or double magazine carrier will conceal just fine, is secure and probably sized to your specific belt width, is quicker to employ with no worries about flaps or snaps or velcro, and most importantly, you can intuitively get a correct hold of the magazine with your finger indexing the front of the mag to guide insertion into the mag well all while not worrying about above mentioned flaps or dumping the second magazine out of the pouch.

JMO.

Glock Sport/Combat mag pouch.





Greatest thing ever! Quintessential GLOCK. To the uninitiated, it seems
like flimsy crap, but nothing could be farther from the truth. It is
rock solid on the belt with no migration and 100% body contact.
Construction is Glock polymer. It is ambidextrous and fits all belt
widths with a clever post cutting system and it weighs virtually
nothing. It has excellent magazine retention as well with a molded in
detent that snaps into the mag catch notch. It also has a generous drain
hole in the bottom to prevent your ammo from being submersed when in
the rain or a body of water.
Anyone that owns a GLOCK pistol would be a fool not to get this,
especially for $10. Another fine product that lives up to its label;
GLOCK Perfection.
The "SM" fits all .380/9x19mm/.40/.357/.45GAP and the "LG" fits all 10mm/.45ACP.




http://www.youtube.com/watch?v=SeTa7Gxw70c




 

When I carry OWB I use Raven Concealment Systems like mag holsters.    I make them myself though.

IWB I just drop one in my pocket.

hmmm...good question.