Grouping phones by area code

I have a list of numbers like :

303102202
303102200
402123212
...

And Im trying to a grouped list. Normally I would say to MySQL

SELECT phone, count(*)
as num_amnt
FROM msglog
GROUP BY phone
ORDER BY num_amnt

And I would get the list grouped by phone. Now, how would I get it to group by area code?

Thanks a lot,
Alex

SELECT substring(phone from 1 for 3),
 count(*) as num_amnt
FROM msglog
GROUP BY substring(phone from 1 for 3)
ORDER BY num_amnt

thanks a lot it worked

SELECT substring( phone
FROM 1
for 3 )
as areas, count( * )
as num_amnt
FROM msglog
GROUP BY areas