Need local advise/suggestions & help on prepaid sim card options for our group of 8 people traveling together upcoming sightseeing trips with stops in 3 cities:

1st stop in HK for 6 days, then flying out to HCMC/Saigon in Vietnam for 5 days, transiting via HKG to PVG/Shanghai for a 6 day tours.

We will have unlocked GSM quad-band phones (non-Android or iPhone) so our plan is to use inexpensive local prepaid sim cards for calling, staying with touch with each other (might be split up into 3 sub-groups) during the day as our interests & plans are a bit different. Is there a sim card that will work at reasonable rates for all 3 cities (didn't look like it as rates/costs are higher in Vietnam ?) Would China Mobile's sim & rates be okay for use in both HK and Shanghai without going thru a new activation/new number, etc. and just refilling it?

One of us will be bringing along a laptop pc, mostly for email & web browsing - directions & restaurants, etc. but we expect to have internet room access at our hotel room (not free in our HK hotel, quoted at $300+ HKD for a 7 day+ access pass) Would one of the recommended prepaid sim with wifi/internet access be a better choice at equal or better price scheme ?
In the past, when I travel out of the country, I use a Motorola Q8 gsm global phone, unlocked to connect to the laptop for anywhere access as long as I get a signal (on AT&T's network) - estimated total usage for this trip should be under 100 MB, certainly nothing greater than 500 MB to 1 GB for all 3 places combined. The Q doesn't have 3G (different bands used anyway) but it will work on Edge speed - an unlocked HTC Ozone (quadband GSM/Vodafone compatiable) phone will be coming along - dual CDMA & GSM band, just in case.

Will not be doing much SMS or international texting on these phones, unless I use the local sim in either the Motorola Q8 or HTC Ozone, both smartphone device but I wanted to keep data access/usage & charges to a minimum if possible. The HTC Ozone is wifi-enabled and I would download when I locate a free hotspots, but not important as long as I can check most emails & messages on the laptop each evening/morning before we go out for the day.

Our hotel in Kowloon is near Nathan Road & Lai Chi Kok Road, and we plan to take the A21 bus from the airport to the hotel stop, with a very short walk - arriving in the early afternoon. So, we should be fine going to a local 7-11 or phone store in town to get the sim cards purchased & activated, instead of doing it at the airport shops, correct ?

Thanks in advance !