Can you paste the dmesg?
Did you install gobiserial driver?
Is the mc7455 working?
You can also have a look on this which is not having AT command port, seems to be similar to your case:
Can you paste the dmesg?
Did you install gobiserial driver?
Is the mc7455 working?
You can also have a look on this which is not having AT command port, seems to be similar to your case: