PLEASE HELP! NEW TO THIS. LG U8120 problems

I have recently got myself this phone (LG U8120) and I'm using a Tesco
SIM card instead of the 3 network. I can send/receive texts and
make/receive calls with my Tesco SIM but I'm unable to send photos.
Every time I try to send a photo it says "Connection failed. Retry?"

I'm not an expert user of mobile phones and find the technology
frustrating (hence the username lol). Please help me (and please avoid
jargon as I don't understand mobiles as well as most of you). Should I
just give-up on this phone?

Thanks for understanding.


--
Frustrated user