EmilF - Thank you! This is exactly the conflicting information I'm finding online. In a dual standby phone, both sims listen for incoming calls all the time. That is clear. The conflicting info I am getting while researching online is what happens to Sim1 when one Sim2 is using 3g to communicate online. As long as Sim1 is always listening for calls/sms/mms while Sim2 is browsing the web or downloading email, then I don't care if Sim2 is turned off for a few minutes if you're on a phone call with Sim1. As long as Sim2 resumes operation automatically once Sim1 disconnects the call.
Using this configuration I will be able to use a 10 cent/min talk sim with an 2GB monthly data sim for half the price of a monthly smartphone talk/data plan from the same provider.
One last question - is it possible in Android to designate Sim2 as the only data sim to be used?
Thank you again!