change native Android SIP dialing settings
I suppose "Prefixer" (written by "253°Below") or another app "PreFixer" can make the job of cutting the "+" symbols from the numbers' beginnings. However you will need to switch the Prefixer off to make the regular GSM calls. Else you can let the Prefixer do a smarter job by cutting pluses only from the numbers which look like "+123....." transforming them into "123.....".

Also there is an application which automatically transforms all the local(short) numbers in the address book into one standard by adding country codes and area codes. Its name is "Contacts Clean-up". It might do a portion of the required job, too.