I haven't tried to use the tool yet, but from a look over the source one suggestion for an improvement is, when getting the contact (remote_ebook_uid ) from the number on the sms you could possibly change the lookup from a full compare of the sms number and contact number to a lookup comparing the last 7 digits of both numbers.

e.g., change line 240 on smsimporter.c from

if (!strcmp (number, remote_uid)) {

to

if (g_str_has_suffix (number, group_uid))

This should allow you to match the contact even if the sms number is in full international format and the contact isn't saved that way.