From what I have read of your post, you seem to have done your research into the subject quite thoroughly.
I use my SGSII all the time for video calls, using the stock dial pad as well as using 3rd party app's such as Skype.
A few things that you should check, (or maybe double check) are...
1. That, first and foremost, you are in a strong 3G/WCDMA
) signal area and that the recipient is also (as this will affect their end of the call). For instance, if I am in a good 3/3.5G
signal area and the person I am calling is not, then the video call will default to audio.
2. Make sure that in Settings > Wireless and network > Mobile networks > Network mode
... that you do not have GSM only selected.
3. That the phone you are calling can actually receive and make video calls. The iPhone 4
cannot receive, by default, calls from phones other than other iPhone 4
's and that is over Wi-Fi only. This is a limitation of the iPhone
. Also, not all Blackberry Bold's
can make/receive video calls, (I do not know of any off hand that can) as with all HTC
handsets. As a rule of thumb, if they do not possess a secondary, front facing, camera it is unlikely that they are video call capable.
4. That your service provider supports video calling and that it is enacted on your account if required. Also that you have the correct APN settings for your service provider in Settings > Wireless and network > Mobile networks > Access Point names.
I hope this helps.