Go for Samsung.
I bought my Samsung GT3530 (something like that) and unlocked it for £10 to use it on Virgin. Very good. The battery charge last for more than 2 weeks easy. (total price for the phone incl unlocked = £40, £10 top up with PAYG)
I also bought a Nokia 3110 (something like that) but the battery charge does not last more than 14 days (2 weeks), which is disappointing but still better than any of the smart phone battery out there where you need to charge almost every hour. (Not unlocked total = £40, £10 top up with PAYG)
I will only use smart phone when the battery charge will last for 2 weeks or more without charging.
😀