[inquisitor]

Originally Posted by Forkedman

I've recently purchased a Tchibo stick (20eu at the moment with the 500mb free) and I want to upgrade to the flat rate plan.

I doubt you can switch to the "Internet-Flatrate XL" during the first month, in which the free "Internet-Flatrate L" is pre-activated. You could try sending an SMS with "STOP DATENFLAT2" to 7777 in order to request cancelation of the current "Internet-Flatrate L". Shortly later you should receive a message requesting your confirmation by sending "ENDE DATENFLAT2" to 7777.
After receiving the final confirmation for your cancelation, send "START DATENFLAT" to 7777 and you will again be asked by another SMS to confirm subscription of the "Internet-Flatrate XL" by sending "JA DATENFLAT" to 7777.

Now, as I understand it, to upgrade to the new plan I need to buy credit (either Tchibo(from the store) or O2 (from all over the place)) and apply this to my account/phone number. Is it possible for me to add the credit via the web, even if I buy it in a store?

At least without a German, Austrian, Swiss or Dutch credit card you can't purchase recharge vouchers online. But O2 vouchers are sold absolutely everywhere.

I ask this because at the moment I don't have a phone, nor do I intend on buying one while I'm in Germany unless I must.

You don't need a phone to manage your credit. If you're using Tchibo's version of Mobile Partner, there should be a button called "Guthaben verwalten", through which you can check your credit ("Guthabenabfrage") or redeem a voucher code ("Guthabenkarte aufladen").

I've noticed that the stick software has SMS features, however when I tried to activate the free 500mb plan all my SMS bounced back or didn't send(I'm not sure which).

Did you receive any error message?

So I'm concerned that I won't be able to activate the credit via the SMS featues on the stick and with my very poor german and lack of a mobile(handy) it's a hassle to activate anything over the phone.

So, I guess I'm asking what my options are here and how I would best go about upgrading to the flatrate.

Beyond SMS and customer care, there's also a USSD-menu (*104#), through which you can manage your tariff options. In order to send USSD-commands with your USB stick, you'll need to download MDMA, fully close Mobile Partner (otherwise MDMA won't work) and then run MDMA, which allows sending USSD commands (*104#).