[Asterisk-Users] Hardware vs. Network Inputs

[Michael Stearne]

We are trying to determine how to build out an IVR system we are
working on.  The system needs to be able to handle probably at most
5-10 concurrent calls at peak times.  Other times we are just looking
for a reliable service.  For incoming calls we've been using
BroadVoice VOIP and before that VoicePulse VOIP.  VoicePulse's IAX
service started dropping DTMF inputs that we were processing soon
after launch and after a few months of reliable service from
BoradVoice SIP, we are experiencing problems catching the digits
(simple 6 digit numbers) that people are inputting.

The question: Is it unrealistic to think that an all network solution
(meaning calls VOIP in to the machine and out from the machine) for
this kind of load is doable?  Or, would it be better to get POTS phone
lines involved with a hardware solution like: 
http://www.digium.com/index.php?menu=product_detail&category=hardware&product=TDM400P
(or a better product)?

If the network approach is possible why are we having so much problems
just capturing the digits people are pressing?  The machine is
connected directly to a T1 that has at least 900kb up and down
available at any time and is 3GHz with decent specs.

What is the problem here?

(Asterisk 1.0.9)

Thanks for any input,
Michael