The Philips BT2500B is one among many inexpensive micro Bluetooth speakers to hit the market in the last couple of years. A lot of speakers of this type have more of a canister design to them, but what helps set this one apart is its relatively flat design, which makes it easy to slip into a bag or even a pocket. It's also modestly priced at around $45 online.
Though you can sit the speaker up vertically, it's really meant to be laid down flat with the driver firing upward. In that sense, it looks like a portable speakerphone and happens to offer that feature as well. I can't say the build quality or all-plastic design are all that swanky, but the speaker looks fairly attractive and has enough heft to it -- it weighs 7.7 ounces -- to steer it away from feeling cheap.
Like a lot of these little speakers, the 3.9x3.9x1.3-inch BT2500B plays louder than its size would indicate, and I liked the analog volume knob, which gives the speaker a slightly retro look and, more importantly, makes it easy to raise and lower the speaker's volume.
That same volume knob can be found on the step-up, which costs around $30 more and is essentially a double-wide version of the BT2500B. It adds NFC tap-to-pair technology for devices that support it, but otherwise the two speakers have identical feature sets and include the standard audio input for non-Bluetooth devices.
It's hard to say which speaker I like better. I thought they both sounded pretty good for their size, though as you'd expect, the larger BT3500 does sound a bit fuller and plays louder; it's clearly the better performer. However, I like the design of the smaller BT2500B. It's literally pocket-size.
These tiny Bluetooth speakers do have their sound limitations, so you shouldn't expect the world from them, particularly in the bass department (it's going to sound restrained with techno and hip-hop, for instance).