What is the problem that the mobile phone can't send MMS? Sending text messages is also very slow.

If you can't send MMS, you should first look at the parameter settings. Some mobile phones are bought back, and the parameters inside are all from the mobile company. If you put in Unicom card, you may not be able to send MMS and surf the Internet. See if the parameters in the mobile phone are consistent with your mobile phone card. The slow sending of short messages may be because you send too many words, and if you send too few words, it will be slow, that is, the cell phone signal is poor.