Asterisk reads numbers incorrectly when external users dial various numeric options

When I call into my main IVR and dial various extensions using my cell phone, or attempt to enter a pin for a conference call using my cell phone, Asterisk sometimes dials the wrong extension, or tells me the extension is invalid, or that the pin is invalid.

I did this with a pin for conference calling and checked the CLI. I correctly entered 5276 each time from my phone. The system showed:
User entered ‘55276’, then
User entered ‘5526’, then on the third try it got it right showing
User entered ‘5276’

This never happens for pins or extensions dialed internally. Is this something I can adjust, fix, optimize? Any help would be appreciated. I’m running and

Some cell phones allow you to extend the length of the DTMF tones they send that should fix it, (some don’t) this is an ongoing problem I have encountered, without about 80 milliseconds of tone on a cell phone, there is little you can reliably do to fix it.

Wow, and here I was thinking it was an Asterisk issue. A quick Google search shows numerous hits of iPhone users having DTMF issues. Well, at least I know it’s not my PBX! Thanks for the info Dicko.