Welcome to OBiLand, noob!
1) the setting is extremely unintuitive and poorly, if at all, documented. First, understand that there are two different ways to change parameters on an OBiTALK device, using a web browser: the device's embedded web server, at some local LAN address, like 192.168.015, or 10.0.0.6, and via the OBiTALK web portal/dashboard. Use the portal, not the local web server. You must get into "expert configuration" mode first. Then, go to IP Phone--> Programmable Keys, and scroll down to Key 7. It should be set to a default function of "Message status". Uncheck both check-boxes to the right of the value, to edit that value. Change it to "Speed dial". Change the Service to SP1, SP2, or whichever SPx you are using for your VoIP service provider's voicemail system.
Change the Number to *97#;Send=Ass*nnnnnn# replacing the n's with your voicemail password. Scroll down and click the submit button and wait for the phone to reboot.
Next, go to the Service Providers --> ITSP Profile x General --> DigitMap, where "x" is the SPx slot you are using (A= SP1, B=SP2, etc.).
Remove the check marks to the right of the value, as before, and edit the digit map, and add *97| after the string's beginning parenthesis symbol. Again, scroll down and submit.
2) Yes, it should work.