Phone buffs, will cheapest I phone meet my needs?

Hoping someone technical can chip their 2p worth in on this.
Would a basic Iphone let me access ebay, my emails, and either download a moneymanager programme or have an excel sheet or similar.
Seen someon ebay in the completed sales and the 8gb ones have gone for around the £60-70 mark. I dont want to pay iphone 4 money for something I will only use for the above
I already have a barred 3gs 8gb so could prob use the spares off this if the screen ever went etc.
I'm on giffgaff which runs on o2 so i have unlimited internet too.
Thanks in advance

Is it a 3gs?
 
I'd really go with the 4 now, to me it makes no sense going for the old tech, I mean I have a 32gb 4 and its slow in comparison to the 4S. I find the 3GS frustratingly slow now but I'd imagine if I didn't know any better it'd be fine haha.
 
Yes overall it will suit all those needs, however if speed is a bother for you then go with the 4. Pretty sure you'll be able to get a decent contract now.

When you say a decent contract mate I currently get 1500 anytime anynetwork mins, unlimited text and unlimited internet for £25 a month payg. Is there a contract deal that would make it worth me juming from this cracking deal??