T400 has to be WWAN ready and to have a unified WWAN antenna already. How do I ensure it is actually there?
I am going to open the top and look if there is empty mini PCI-E connector.
What should I be looking for?
If you remove the keyboard there should be two antenna cables where the slot for the WWAN adapter is. Depending on model and antanae configuration, there will either be 2 wires black and grey, or 3 wires black, grey, and white used for the 802.11 wifi wireless card. If the model is also prewired for WWAN, there will be a red and blue set of antenae wires.
You could also start "msinfo32" and check out the "system model" field under "system summary". It should contain the exact type/model no. Did you remove the sticker under the computer with the model number? You will also find this info by using the "wmic computersystem" command from command prompt.
Additionally, If your laptop is wwan ready, then there should a wireless icon on the LED bar next to the wifi bar.The empty slot is under the ctrl+Fn location under the keyboard/
Also, the sim slot under the main battery compartment will confirm whether your laptop is WWAN ready or not.