1）I was glad to be like my friends which all had mobile phones.
改为：I was glad to be like my friends （who ）all had mobile phones.
2）I became an expert for sending fast messages.
改为：I became an expert（ in ）sending fast messages.
3）I often think my old phone will make people to laugh.
改为：I often think my old phone will make people laugh.(去掉 to)
4）Most of the time it turned off.
改为：Most of the time it （was,is ）turned off.