Unlock mobile phone from the three network a...

it can get switched off during voice communication

Here in the UK most markets (out door street type) will have a stall who will unlock most handsets for about 5gbp (or 10usd) you could also ask three themselves to give you the unlock code, they do so here in the UK and europe. Tell them you are to travel abroad and wish to use a local sim card to make calls. Also do a google search for "A1K" and go to the site at top of list "machman" they have downloads of firmware which is unlocked.