Hello Tpoon,
Welcome to the community!
From what you describe, it sounds like you could be referring to two potentially separate issues: not being able to send MMS and your phone only showing 3G (ie not getting 4G or LTE).
Firstly, the 4G/3G/2G Mobile Network option you note is the same as GSM/WCDMA/LTE (auto) (except in reverse). Long-Term Evolution (LTE) tends to be a North American term for the same technology the rest of the World calls 4G. As such most phones purchased from outside of North America will show 4G when connected to the LTE network. I understand 4G occasionally refers to a data connection to the WCDMA network using the HSPA+ protocol. However, the phones purchased outside of North America will usually show H+ rather than 4G for such a connection.
As far as I am aware, the Hong Kong version of the LG G6 is the H870DS. Could you please confirm this version is the phone you have? Assuming it is the same version, that phone would have all of the compatible bands/frequencies for 2G and '3G'. With regards to LTE, that phone would have 3 of the compatible bands/frequencies. You can also verify the compatible bands/frequencies here.
The H870DS is a dual-SIM phone. Could you please confirm whether you're using one or two SIM(s)? If you're using one SIM, which slot is the SIM using?
More specifically, that phone is a dual-SIM, dual-standby phone. That means only one SIM is active at any given time. The other SIM is in standby-mode. Depending on how the manufacturer designed the phone, both SIM-slots may or may not have 4G (LTE)-capability. There are conflicting reports as to whether both SIMs are capable of 4G on the H870DS. You will have to contact LG HK for clarification on its functionality. That said, most newer dual-SIM phones will have 4G-capability on both SIM slots. However, since the phone is dual-standby, only one slot will be capable of data at any given time. The other slot (stand-by) will only be capable of voice and SMS (3G or 2G).
Since the phone is LTE-capable, it should be using ltemobile.apn. You can verify the settings in the link FidoPamela provided above. Each SIM-slot may have their own APN settings.
Are you able to use data at all? Sending and/or receiving MMS would require data to be enabled. You might also consider trying to enable roaming data. Some phones from abroad might think they are roaming even though they are using a local SIM.
Hope this helps 
Cheers
Hey @Tpoon!
Welcome to the Community
Did you add the settings for the MMS as well? You can find all the settings to add right here on our blog.
To access LTE, the device must be compatible with one or more of the following:
- 700 MHz on Band 17;
- 1700/2100 MHz on Band 4;
- 2600 MHz on Band 7.
Did you check with the manufacturer to see if that's the case with your phone?
Let me know!
