Measuring usage of a prepaid mobile subscription (Vodafone CallYa Germany)

I need your help regarding a little bash script,
the webpage returns the following Values:
Total Volume: 750 MB or 1 GB (or even more) (its mb2 in the script, at the moment it’s 1GB so gbtotal*1024)
Available Volume: 1 GB (0% Used) or xxx,y MB (usage started)

How can i switch between GB or MB for the used volume?
(For the total volume i convert it in MB)

The values are exported, seperated with a dot, because the webpage uses european locales (comma)

This is the relevant section:

	sed -n  -e 's/^.*Highspeed-MB.*> \([[:digit:]]*,*[[:digit:]]*\).*$/\1/p' $callya_file | sed -e 's/,/./g'