Noob to Asterisk, quick help on dial plan for Callcentric

Kindly requesting anyone to help, or point me in the right direction. I am still confused about dial plans in extensions.conf.

I’m running Asterisk 1.4 connecting to Callcentric. I’ve got everything working great except Callcentric apparently only allows 10 digit dialing. I’d like to be able to dial using the following

1 followed by area code and 7 digit number
7 digit number (inserting my local 650 area code)
011 for international calls
911 for emergency calls, etc

I’ve got the following dial plan which does everything except the 7 digit number with automatic insertion of my local area code. Could you look at my dial plan and suggest what needs to be changed?

exten => _1XXXXXXXXXX,1,Dial(SIP/${EXTEN}@callcentric)
exten => _011X.,1,Dial(SIP/${EXTEN}@callcentric)
exten => _911,1,Dial(SIP/${EXTEN}@callcentric)

Thanks in advance,

_XXXXXXX (no dot)

Many thanks,