In my own opinion, if you're upgrading from 8100..I will go to 8320 but if you could find unlocked 8310.. The GPS feature works for everyday use (specially if you're in field work). both phone can be upgraded the external memory (micro SD). but if I have a budget I will go to BOLD. The best thing to choose a cellphone is look for the specification and check which features will fit on your needs. the reason is, if you bought a cellphone who has a lot of features and you're not using its features, its a waste of money. its like you bought High end computer and you're using it only for word processing. I hope this will help you to choose which phone is better for you.