Hi there, sorry to reply and necro the thread.
I just restored my K750i - bought in 2006. 14+ years ago . Was sleeping for 10-11 years (based on last call and SMS records  )

How I charge the phone is I use an external battery charger :

https://shopee.com.my/-Ready-Stock-Mobile-U...6414.4275322180

There are several variations also. But I chose this only because it can accomodate the largest possible battery.
Works for all handphones with external battery.

I might order a K750i charging and data cable from Shopee.
https://shopee.com.my/USB-Charging-Cable-Fo...8813.2548643391

Hope you are still keeping the phone!

Hi Raikkonen,
The reason I revive the phone is because of fond memories.
Just imagine the 1GB M2 Memory card still works until today. Photos and videos I take 10 years ago still remain.
Yes I do have 4G smartphones also. Undeniably Samsung is the most reliable followed by Huawei.

I managed to get the battery from a Kelantan seller.
https://shopee.com.my/%F0%9F%8C%9FClear-Sto...4675.5473184883

RM 9.80 for a new battery. Cheapest offer I've seen! 

Currently I am using Yoodo as the cheapest way to maintain the line (my exisiting line) . Secondly Yoodo supports Call Forwarding - very useful, if someone calls the number and no signal , it will auto forward to another line (must have Call minutes add on)

Only issue is that - the 2G reception is rather weak on Yoodo in this phone. Very sensitive to Indoor reception. 

At first I tried with DIGI the 2G signal is stronger. But more expensive if just want to maintain the SIM card.
(They have an option - Reload RM 110, pay RM 108 for 1 year. Just to maintain the line. Not inclusive calls or anything) 

Its probably the smallest smartphone (okey, its not Android, but at least it had Java support) .
But think of it: 14 years ago, it was considered a very advance phone.

From 2G to now upcoming 5G. We have come a long way.

Hi Raikkonen,
So far I have tested my K750i with a new battery, for a old smartphone , with standby time of 4 days over and still remain 28%, so it does quite well.
I might try buying a signal booster - 5 Pcs from China cost only less than RM 4, to improve reception.

https://shopee.com.my/%E3%80%90remitglory%E...4408.7025095271

Okey, here is what you are looking for. SE connector convert to earphone jack:

https://shopee.com.my/Sony-Ericsson-Audio-C...9413.8603754024

Thankfully still got sell Sony Ericsson handsfree, which need to import from Indonesia

https://shopee.com.my/Handfree-Sony-Ericsso...0500.7169777466

Sadly, Malaysian seller sells SE Handsfree at exorbitant prices..up to RM 60 even.

There...I've listed several links to help to restore back the good ol' K750i. A classic which needs to be restored.