how can I use my old phone's features w/o sim card?

It’s all in my subject line, but basically because of my profession I was pushed into the age of smartphones with not very "smart battery life. The thing is, in almost every way that my phone doesn’t require a good camera or computer-like functionality, my old phone is better. It has plenty of features I wouldn’t mind having access to. And more importantly it would be working from a separate battery to do things with it. I don’t want to make calls with it, but I wouldn’t mind using the calendar, or the calculator function, the mp3 player or the pedometer built into it when I exercise. This phone is an Sony Ericsson though and when the SIM isn’t present the whole phone is inaccessible for use. Is there a way to “trick” the phone into just giving me access to the device’s feature set sans-phone functionality? I’d be willing to get one of those cheapo,$10 phone sims and not use the service if just having A SIM is the only requirement, but would rather spend no money at all to be able to use the other areas on my phone. Any tricks? It’s not really worth anything to sell it, but it’s ridiculous to have to keep switching the sim between phones. What are my options?

You don’t have one - the phone does not function without a SIM. It is the way it was constructed. Get a cheap PAYG SIM, and leave the phone in AirPlane mode so you cant make calls.

I use a smartphone to run a navigation program, needs a sim card but its not even activated and works fine.

Your smart phone almost certainly has all those functions though(or you can download an app that lets you do so, most likely for free). So why?

I think the OP doesn’t want to use up the battery of the smartphone doing all those other things. But you’re right: Instead of carrying around two phones, just carry around one or two extra batteries, so you can do everything on the smartphone.

You have an old phone lying around, but don’t have any old SIM cards lying around? They don’t need to work/be active.

Ask your friends. Give it a couple of weeks, then ask again, because it will take them a couple of weeks to find/notice the old SIM card in the bottom of the drawer.